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Washington, D. C. October, 1928
THE AIR SEASONING OF WESTERN
SOFTWOOD LUMBER
By
B. V. FULLAWAY, Jr., Formerly in Charge Office of Forest Products
Missoula, Mont.
HERMAN M. JOHNSON, Assistant in Forest Products
Portland, Oreg.
and
C. L. HILL, In Charge Office of Forest Products
San Francisco, Calif., Forest Service
UNITED STATES
GOVERNMENT PRINTING OFFICE
WASHINGTON
1928
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER
By 8. V. Futtaway, Jr., Formerly in Charge Office of Forest Products, Missoula,
Mont., HERMAN M. JOHNSON, Assistant in Forest Products, Portland, Oreg.,
and C. L. HILL, im Charge Office of Forest Products, San Francisco, Calif.,
Forest Service
CONTENTS
Page Page
PELE OGUCEION ais ee eee eer nai el PIL BO Lh a i) |) Aur-seasoning practice aasasceesnecee seen eee 13
Important principles of wood drying and their May Ghavabatee nl OT se 13
PEneralvap pl Cations we se ayaa 3 Segregation of stock for piling. _--________- 22
Occurrence of moisture in wood__________- 3 IPile;constrUctione Bae Ou yee en Deena 23
Movement of moisture in wood___________- 4 Summary of methods for improving drying
Effect of humidity on drying______________ 5 EAC ECE ei a0 es Ch OI a a pe We
Effect of temperature on drying__________- 6 | Regional air-seasoning problems and their solu-
Effect of air circulation on drying_________- 6 GLO CU ta Wa Tn I icra aoe Norell el 43
Conditions outside of the pile that influence Inland Empire pine region____-__-_---___-- 43
AlTESCASO MIN Beane eh ee etd 6 California pine regions == ee 49
Circulation of air within the pile__________ iG Riedwoodiregion eS ee 51
Causes and control of stock depreciation... 9 Douglaswirregion= 2220 ee ee 54
| INTRODUCTION
_ A real need exists in the lumber industry for a concrete presen-
tation of efficient air-seasoning methods for western softwood lum-
_ ber, including a review of the general principles that govern the
_ drying of wood and their application to yard drying. Air-seasoning
losses in the West, both in quantity and quality of the product,
can be reduced. The average drying time can be shortened, with
a consequent faster overturn of stocks. Shipping weights can be
lowered and final moisture-content requirements more nearly at-
tained. Moreover, highly competitive conditions in industry make
essential all practicable improvement and economy in lumber manu-
facture, as well as a product of the highest possible utility and one
that meets consumer requirements satisfactorily.
The import of such considerations to the lumber industry of the
West is evident in view of the fact that 35 per cent of the total
annual cut in its four‘ principal producing regions is air seasoned,
or approximately 4,500,000,000 board feet, at a rough valuation of
$120,000,000.
1 Douglas fir region of western Oregon and western Washington, “Inland Empire,”
California pine region, and redwood region.
1
yi DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
TABLE 1.—Average annual production of western sofiwood lumber by regions *
[In millions of board feet]
Douglas aioe Califor- tape S
Kind of wood fir ping nia pine | “Vooq | Total
region region region region
Incense cedar ((Libocedrus decurrens) --=---- 222 ee oes eee ee S24. s eee 32
Western red cedar (Thuja plicata)--------------------- 218 Ba" | ioe le en 251
Douglas fir (Pseudotsuga taxifolia) - -..-.-------------- 6, 539 292 103 104 7, 038
\Willlnie Wine. eee ee eee se se seceeissseos 17 73 183 16 289
Western hemlock (Tsuga heterophylla)?__.__---------- 819 Qi Soa eee il 829
Western larch (Larix occidentalis) ._..------------------ 1 212) 22S se es | See 273
Lodgepole pine (Pinus contorta)___-..-----------------|--------.- GSE pie ate eee |) eT aes 5
Sugar pine (Pinus lambertiama)*___~-_.---------------- S fwieyee went 14ik a eee 229
Western white pine (Pinus monticola)§__-..-_.-------- 1 BL OR pe Mecca Men senha er 394
Western yellow pine (Pinus ponderosa)®___-_-_.------- 16 1, 023 846 2 ee seen 1, 885
Redwood (Sequoia sempervirens) ----------------------|-------- go|[exees222)a/sebse054 536 536
Sitka spruce (Picea sitchensis) _-_---------------------- BE fl ie eset WR BE 5 2 339
Engelman spruce (P. engelmannii) ---~----------------|---------- DON ao een | eee 25
MPotaly Ae PHOT aU a PA YON Th Se ee 7, 956 2, 125 1, 378 659 | 12,118
1 Figures (rounded) based on five-year production records; Douglas fir region includes western Oregon
and Washington; Inland Empire pine region includes Montana, Idaho, eastern Oregon and eastern _Wash-
ington; California pine region includes California, Nevada, and Clamath Falls district of Oregon; Califor-
nia redwood region includes redwood belt in California. ;
2 Includes the following species: White fir (Abies concolor), lowland white fir (A. grandis), silver fir (A.
amabilis), red fir (A. magnifica), alpine fir (A. lasiocarpa), and noble fir (A. nobilis).
3 West Coast hemlock.
4 California sugar pine.
5 Idaho white pine. : : ;
6 Pondosa pine, California white pine.
The air seasoning of lumber is, however a complex problem if
anything like real efficiency is to be obtained. In working out the
proper solution five distinct objectives must be kept constantly in
mind:
1. Minimum depreciation of stock.
2. Rapid rate of drying.
3. Low, uniform final moisture content.?
4, Economy in operating cost.
5. Reasonable yard space.
Other complications of the problem must also be recognized. The
various species, grades, and sizes of stock require individual con-
sideration. Owing to climatic and other differences, the answer for
one yard will not always hold for another. The effects of seasonal
weather variation must also be provided against by each yard sepa-
rately.
Reon attainment of any one of the five principal objectives
may often preclude the full realization of the others. Since actual
efficiency in air seasoning must in the final analysis be measured by
the profit-and-loss yardstick, it is necessary that these five objectives
be adequately balanced to the best advantage of the producer.
2The fact that wood shrinks and swells with changes in moisture content makes it
highly desirable that seasoning result in a final moisture content suitable for the condi-
tions of final use, but absolute attainment in this direction is hardly possible on account
of the varied purposes for which wood is employed and the wide range of atmospheric
conditions under which it is used. This can be illustrated in a concrete way. Wood
thoroughly air-dried has a moisture content at Galveston, Tex., of about 17.5 per cent
and at Phoenix, Ariz., of 7.5 per cent. In the general Middle West territory wood, to
give the most satisfactory results, should have a moisture content of 6 to 8 per cent for
interior work and 12 to 15 per cent for outside use. These differences indicate forcibly
that the final moisture-content problem is a difficult one, but they also emphasize its
importance to the operator.
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 3
A great variety of air-seasoning methods have come into use dur-
ing the long period of development in the lumber industry. Obser-
vations of much value have been accumulated by those of experience
in the industry; and yet to-day, after many years of air-seasoning
practice, a wide difference of opinion exists among operators as to
the relative value of many of the basic principles involved. There
is urgent need for authentic and usable information based on careful
studies.
It is obvious that the solution of the air-seasoning problem can not
be found in any set of “cut-and-dried” rules. ‘The chief aim of
this bulletin is to present those general principles which can be
applied by the lumberman in the manner that will best meet his own
specific conditions and problems. No attempt is made to present
the detailed data in substantiation of the conclusions given. The
conclusions are based on surveys and study of current practice and
on intensive air-seasoning investigations by the Forest Service within
the four western lumber-producing regions.?
IMPORTANT PRINCIPLES OF WOOD DRYING AND THEIR
GENERAL APPLICATION
OCCURRENCE OF MOISTURE IN WOOD
Moisture in wood, or sap, is chiefly water with small percentages
of organic and mineral matter present in soluble form. In the sap-
wood these materials are largely sugars, but in the heartwood they
are principally tannins, resins, and dyestuffs. For all practical
purposes in the drying of wood sap can be considered as water,
since only very small quantities of the other materials pass off in
evaporation.*
3 Acknowledgment is made by the authors to other members of the Forest Service, par-
ticularly those of the Forest Products Laboratory, who have contributed in a large
measure to present knowledge relating to the principles of drying wood. Acknowledgment
is also made to C. Burdette Green, formerly a member of the Forest Service, for his very
considerable contributions of air-seasoning data from California.
4The amount of moisture in wood, or the moisture content, is expressed in terms of
percentage of the oven-dry weight of the wood. Thus, if the moisture content of a green
board is 71 per cent, there are by weight 71 parts of water to 100 parts of oven-dry wood.
Similarly, should the moisture content of a board happen to be exactly 100 per cent, the
weight of the moisture and that of the oven-dry wood would be equal. The average
moisture content of a lot of lumber may be determined in the following manner:
Select representative pieces—about 1 out of every 100 to 500 pieces—with a fair repre-
sentation of both heartwood and sapwood.
At a point about 2 feet from one end of each piece, cut out a section three-fourths to
1 inch wide, making the cut at a place free from knots, rot, pitch streaks, or other defects.
Trim off all slivers from this section or sample. Sy
Weigh the samples immediately and carefully on a delicate balance. This is the
original weight.
Place samples in an oven heated to 212° F., or, if an oven is not available, on hot steam
pipes; but do not scorch or bake them. : 4
When samples have reached a constant weight, as can be determined by repeated weigh-
ing, remove them from the oven. (After a little experience the time required to reach
constant weight can be estimated, and thus repeated weighings may be avoided. Twenty-
four hours should be the maximum time necessary with softwoods.) This final weight is
the oven-dry weight. ; c f 4
Subtract the oven-dry weight from the original weight. The difference is the loss in
moisture.
Divide the difference by the oven-dry weight and multiply by 100. This gives the per-
centage of moisture contained in the wood based on the oven-dry weight.
EXAMPLB
Original weight =284.7 grams.
Oven-dry weight—180.2 grams.
284.7 grams—180.2 grams=104.5 grams, or the moisture lost.
104.5 +180.2=.580 X 100=58.0 per cent moisture originally in the wood.
(For convenience and accuracy the gram is often used as the unit of measurement, but
other units, such as the ounce, may be employed.)
4 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
Moisture is held in green or wet wood in two ways. It is con-
tained within the otherwise practically empty cell cavities, and it is
absorbed in the cell walls. The cell water is called “ free” water;
that in the cell walls may be termed “imbibed” water. Free water
is found in the cell cavities only when the cell walls are fully
saturated.
Shrinkage of wood takes place only with a loss of moisture and
swelling with the absorption of moisture. But all loss of moisture
is not accompanied by shrinkage. As wood dries, it first gives up
its free water. After the cell cavities become empty, the moisture
in the saturated cell walls is drawn off. Wood does not start to
shrink until the cell walls begin to lose moisture.
The point at which the cell cavities are empty but the cell walls
are still saturated is thus an important one in drying. It is known
as the fiber-saturation point. The moisture content at this point
varies from 20 to 35 per cent, but for most woods is between 25 and
30 per cent. In actual practice, of course, the cells near the surface
fall below this point before those on the interior have reached it,
and the outer wood tends to shrink before the inner. Such a state
is often the cause of serious drying troubles.
Free water is present in both the heartwood and sapwood of most
living trees but in greatly differing quantity. Sapwood usually con-
tains more moisture than heartwood. Butt logs ordinarily have a
higher moisture content than top logs. Contrary to common belief,
the quantity of moisture in green wood has little seasonal variation.
Species and locality of growth, however, have an important bearing
upon it.
Variation of moisture content was very marked in the many de-
terminations of green wood made in the air-seasoning investigations
upon which this study is based. Differences between species were,
of course, large, but in all species the select grades contained more
moisture than the common grades, owing to the greater proportion
of sapwood in the better class of stock. The moisture content of
western white pine averaged about 84 per cent for selects and 75
per cent for common; that of sugar pine 190 and 75 per cent; that
of white fir 200 and 90 per cent; and that of redwood 200 and 70
per cent. The moisture content of coast Douglas fir probably
ranges from 53 to 32 per cent and that of western hemlock from
120 to 28 per cent. Variation resulting from locality of growth is
well illustrated by the moisture content of western yellow pine. The
moisture content of stock from California ranged from 185 to 100
per cent, whereas that in stock from the Inland Empire ranged from
115 to 80 per cent.
MOVEMENT OF MOISTURE IN WOOD
As already stated, wood upon drying loses first its free water
and then that which is absorbed in the cell walls. The pores them-
selves have very little to do with drying or the movement of moisture
in wood. The moisture does not flow out of the pores of wood to
the surface, but comes to the surface only along the cell walls. Thus,
because of the nature of wood structure, the end grain of wood loses
moisture more rapidly than does the side grain, and flat or plain-
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 5
sawed faces lose it more rapidly than do vertical-grain or quarter-
sawed faces.
For an understanding of the air-seasoning process, this general de-
scription of the movement of moisture in wood is sufficient. It can be
assumed that the moisture tends to distribute itself evenly through
the wood, moving from the moist regions to the drier ones. The
really important facts are that the temperature and humidity of the
atmosphere at the surface of the wood are controlling factors, and
that circulation of the air is of extreme importance in maintaining
and modifying these.
EFFECT OF HUMIDITY ON DRYING
Wood possesses the property of giving off or taking on moisture
from the surrounding atmosphere until the moisture in the wood
comes to a balance with that in the air. The humidity or water
vapor in the air is, therefore, very important in the drying of wood,
and a general understanding of this relationship between humidity
and moisture content of wood is essential.
The weight of the water vapor contained in a cubic foot of air
is the absolute humidity and is usually expressed in number of
grains. This does not, however, indicate the drying capacity of the
air, for the ability of air to hold water, or its saturation point, varies
greatly with the temperature, as is illustrated by Table 2. This
ability of air to dry wood, or any other substance, varies according
to the additional moisture it can hold before becoming saturated.
The vapor in the air expressed as a percentage of the saturation point
for the same temperature is called the “ relative humidity ” and indi-
cates the comparative drying capacity of air. The lower humidi-
ties represent dry air and the higher ones moist air. As used in this
bulletin, the term “humidity ” alone refers invariably to relative
humidity.
TABLE 2.—Cubic foot moisture capacity of air at different temperatures
Temperature} Moisture
STR, Grains
20 1. 24
40 2. 86
60 5. 80
80 11.10
100 20. 00
Marked changes in relative humidity are evident from season to
season, and also the usual daily fluctuations must be taken into
account. Because of its tendency to come to definite balance with
the surrounding air wood is, under ordinary atmospheric conditions,
practically always undergoing at least slight changes in moisture
content. This same tendency accounts for the differences in final
moisture content of thoroughly air-dry wood at different times of
the year. The pick-up in moisture content of lumber left piled in
the yard over winter is likewise explained. ‘Table 3 shows the ulti-
mate moisture content of wood if kept under exact humidity and
temperature conditions.
6 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
The rate of drying depends largely upon the relative humidity.
At a low humidity, evaporation is rapid; at a high humidity, it is
slow. Relative humidity alone, as indicated, does not altogether de-
termine the rate of drying. The temperature and the circulation of
the air also influence the rate of evaporation.
Taste 3.—Ultimate moisture content of wood at different temperatures and
degrees of relative humidity *
Moisture content at three
Rela- temperatures
tive
humidity
70° F. 140 °RR a 21200 Re
Per cent | Per cent | Per cent | Per cent
2 : !
0 4.5 3.3 2.2
30 6.0 4.5 2.9
40 bo 5.9 3.9
50 9.3 Want 4.9
60 11.2 8.8 6.2
70 13.5 10.7 8.0
80 17.0 14.0 10.5
90 22. 2 18. 2 14.0
100 32. 0 26. 2 21.0
1 Prepared by the Forest Products Laboratory, Forest Service.
EFFECT OF TEMPERATURE ON DRYING
The temperature of the air surrounding wood affects drying in a
number of ways. Heat is always consumed when evaporation takes
place, and must be continuously supplied by the air, if evaporation is
to be kept up. Also, as has been pointed out, an increase in tempera-
ture of the air increases its capacity to hold moisture and thus
hastens evaporation. Below the fiber-saturation point a greater de-
gree of heat is required to separate water from wood, this require-
ment increasing as the wood becomes drier.
These effects of heat or the temperature of the air upon the drying
process explain certain conditions encountered in air seasoning. For
example, even during the coolest months of the year, loss of moisture
is comparatively rapid until a moisture content of about 30 per cent
is reached, which corresponds to the fibre-saturation point. Then
an abrupt decrease in the drying rate takes place.
EFFECT OF AIR CIRCULATION ON DRYING
Air circulation plays a big part in the drying process. As wood
dries and evaporation uses up heat and increases the amount of
moisture in the surrounding air, circulation of air is required to sus-
tain the supply of heat necessary for evaporation and to remove the
evaporated moisture. Circulation is thus a real factor in the drying
of wood by any method and is particularly important in air
seasoning.
CONDITIONS OUTSIDE THE PILE THAT INFLUENCE AIR SEASONING
Since the air seasoning of lumber is dependent upon the tempera-
ture, humidity, and circulation of the surrounding air, regional
climatic conditions, modified as these are locally by elevation, topog-
OE ~
THk ATR SEASONING OF WESTERN SOFTWOOD LUMBER 7
raphy, drainage, and bodies of water, constitute the primary in-
fluences in air drying. No matter what the yard methods, nor how
efficiently air-seasoning practice is designed to control the drying
conditions within the lumber pile, a warm, dry, windy climate will
cause faster drying and lower final moisture content than will a
cool, damp, calm climate.
The considerable variation of geographic and climatic factors be-
tween the several western lumber-producing regions and also between
yards in the same region, and the influence of such variations upon
the air-seasoning process are clearly illustrated by the data in Figures
7 to 10 showing the effect of different weather conditions upon the
actual drying. Even though these natural conditions are subject to
little control, a knowledge of them and recognition of their effects on
drying are essential to the intelligent selection of a yard site, the
proper laying out of the drying yard, and the development of effec-
tive piling methods.
The aim of air-seasoning practice must necessarily be to employ
the favorable natural elements to the greatest possible advantage and
to minimize the effects of the unfavorable elements. Granted that
absolute control of drying conditions is impossible, much can yet be
done if the general principles and objectives of drying are understood
and properly coordinated. For example, a certain amount of heat
is transmitted to the lumber from the direct rays of the sun, which
reach at least a part of the pile during some portion of the day. The
outside area of the pile which receives direct sunlight as well as the
length of the daily period during which the sun can reach the sides
or ends of the pile can be controlled to some extent by such methods
as varying the spacing at the sides, front, and back of the pile and
determining the direction of these openings,
CIRCULATION OF AIR WITHIN THE PILE
The functions and importance of circulation in air seasoning have
already been indicated. Circulation of air is the only drying factor
that is subject to direct methods of control, and, in turn, it largely
controls the effects of heat and humidity within the lumber pile.
The movement or circulation of air in a lumber pile is of two gen-
eral types. Horizontal circulation is dependent upon and is caused
primarily by the local wind currents. Vertical circulation, on the
other hand, is an individual internal movement.
Horizontal circulation can be regulated to some extent by, yard
layout, foundation construction, and piling methods. Arrangement
and spacing of pile alleys, rear alleys, and the intervals between piles
on the same alley directly affect the movement of the local air cur-
rents. Likewise, the clearance under the pile foundations exerts an
appreciable influence. And the actual inlet and outlet of the wind
currents to and from the pile are greatly affected by the method of
pile construction.
Vertical circulation in the lumber pile is a drying factor of the
utmost importance and should be thoroughly understood. As the
green stock in the pile dries, the evaporation uses up heat. The air,
thus becoming cooler and heavier, tends to drop gradually toward
the bottom of the pile. Pile construction should therefore be de-
8 DEPARTMENT BULLETIN 1425, U. 8. DEPT. OF AGRICULTURE
signed to aid this natural movement, permitting as far as possible
an unobstructed and continuous downward flow of air. To obtain
benefits from vertical circulation, it must be positive, and not only
at a single point but throughout the pile from one side to the other.
This makes it essential that vertical air channels be ample and well
distributed.
This natural downward movement of cool, moist air in a lumber
pile results, however, in stagnation and slow drying in the lower
section unless proper means are provided to insure the removal of
such air. Therefore, horizontal circulation, particularly in the lower
portion of the pile and beneath it, is a necessary adjunct to vertical
circulation. If adequate means for circulation both in the yard and
in and under the pile are provided, the air cooled and laden with
&0
woh FILE DESCRIPTION
STOCKS NE NTE N02 CUVION HESTERN HHITE PINE
BOX’ TVPE PILES
16 FEET SQUARE -110 COURSES
60 —_ I XF CROSSLRS
Wy 2° SPACING BGLIMWELN BOARLS
Moisture content, per cent
8 S 3
LN}
Ss
10
oO
43 20 27)\ 3 /0 (7 24) 3 i V22, 239 iS 12 19 26)\ 3 70 17 24 FW\\P
DEC.
AUG. SEPT. OCT. NOK JAN.
Fic. 1.—Comparative rate of drying in different parts of typical lumber pile
moisture by evaporation is replaced by warmer and drier air from
the outside. This movement toward the outside of the pile is made
possible by wind currents and to a lesser degree by the natural out-
ward flow in the lower portion of the pile caused by the pressure of
the downward movement.
There is much misconception of the nature of air movement in a
lumber pile. If the natural tendency of the moist air to drop toward
the bottom of the pile is not adequately provided for, drying in the
lower part of the pile will lag behind that above, and serious drying
troubles are almost certain to develop. The average drying time will
be lengthened, a portion of the stock may never reach a thoroughly
air-dry condition, and in pine lumber the liability to stain develop-
ment will be increased. ‘This lag in drying is well illustrated in
Figure 1, which represents actual drying conditions in different parts
of a typical lumber pile.
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 9
CAUSES AND CONTROL OF STOCK DEPRECIATION
The defects in lumber resulting from air seasoning are very
definitely related to methods used in the drying process. An under-
standing of their causes will permit a better appreciation of the
possibility and means of prevention. These defects may be grouped
as those due to shrinkage and those due to fungi. Shrinkage de-
fects include check, cup, warp-bow-twist, and loosening of knots.
Defects caused by fungi include stains and decay.
SEASON CHECKS
Lumber checks as the result of uneven shrinkage. This, in turn,
may be due to one or both of two causes, uneven drying or the in-
herent difference between radial and tangential shrinkage in wood.
Uneven drying is due commonly to the end grain of wood giving
off moisture more rapidly than the side grain, to surface layers dry-
ing faster than those on the interior, or to the fully exposed portions
of the board drying before adjacent sections not so exposed are able
to lose their moisture.
Tangential shrinkage, or shrinkage in the direction of the rings,
is on an average about twice as great as radial shrinkage or shrinkage
across the rings. Table 4 gives this differential in shrinkage for
each of the commercial western species.
TABLE 4.—Radial, tangential, and volume shrinkage* of different woods from
the green to the oven-dry condition, in percentage of green size?
Shrinkage Ratio Shrinkage Ratio
ea of of
1 tan- tan-
Western species Tan- tot 5 Western species Pine ean *
sok Radial] gen- | radial pe Radial] gen- | radial
tial | shrink- tial |shrink-
age age
Per Per Per Per Per Per
cent cent cent cent cent cent
Incense cedar______-- 7.6 33 Bei HOI AAWan ey The eee See 10. 2 3.4 7.0 2. 06
Port Orford cedar____| 10.7 5. 2 8.1 1.56 || Western hemlock____} 11.6 4.5 7.9 1.76
Western red cedar -__- 8.1 74515 Orel! 2.04 || Western larch_______ 116}, 4.2 8.1 1. 93
Douglas fir, Rocky Lodgepole pine_____- Ti) 4.5 6.7 1.49
Mountain_________ 10.6 3.6 6.2 R77 Ni shureeehe poyboYe ee 8.4 2.9 5.6 1. 93
Douglas fir, Pacific Western white pine_| 11.5 4.1 7.4 1.80
LOOSE Esta AEG. 12.6 5.0 7.9 1.58 || Western yellow pine_} 10.0 3.9 6. 4 1. 64
Siliverifire 22-22 - 2k 14.1 4.5 10.0 DL ODIN URANO ROO ee 6.3 all 4.2 15
Lowland white fir___| 10.6 3.2 7.2 2:25 || Sitka spruce_________ 11.2 4.5 7.4 1. 64
IVObD emir es sai ek 13.6 4.8 9.1 1.90 || Engelmann spruce_-_-_| 10.4 3.4 6.6 1. 94
1 Radial shrinkage is at right angle to the annual growth rings, tangential shrinkage is in the direction of
the growth rings.
2 Data by the Forest Products Laboratory, Forest Service.
The end checking of lumber during air seasoning is very largely
due to the uneven shrinkage which results from the exposed ends
drying more rapidly than the adjacent portion. Not only does the
end grain normally give off its moisture more rapidly than the side
grain, but the side grain at or near the end of the board is covered
top and bottom by the crosser and so is not exposed to the air. It
follows that, to minimize end checking, ends of stock should be
109391°—283——2
10 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
shaded to decrease the rate of drying, and the area covered by the
crosser should be reduced as much as practicable.
Season checks appearing on the faces of the stock result both
from uneven drying and from the differential between tangential and
radial shrinkage. With excessively rapid surface drying, the outer
layers become much drier than those on the interior and tend to
shrink before the inside portion is dry enough to do so. Stresses
are thus set up in the piece which may cause checking either im-
mediately or when the stock is run through the planer. Other stresses
are set up when one section begins to shrink before an adjacent one
is sufficiently dry to do so, and these result in checking in the drier ©
section. Crossers are often responsible for this type of check in the
stock. In plain-sawed pieces the face of the board nearer the heart
of the tree is more subject to tangential shrinkage than the other
face, and although the resultant tendency to cup is met by the weight
of the pile holding the boards flat, the stresses set up may result in
checking. The prevention of excessively rapid drying tends to reduce
any form of checking, and a decrease in the area covered by the
crosser will also aid materially.
CUP
The cupping of lumber may be caused by one side drying and
shrinking more rapidly than the other, as when stock is piled two
layers to the course and the exposed faces are dried to a lower final
moisture content than is the other face. It may also be due to one
side shrinking more than the other even when uniformly dried, as
in flat-sawed lumber; in flat or tangentially sawed lumber the side
toward the center of the tree shrinks less, causing the lumber to cup
away from the center. In general, cupping may be held to the
minimum by the prevention of too rapid drying and by allowing both
faces of the stock to dry evenly.
WARP-BOW-TWIST
Warp-bow-twist is usually the result of uneven shrinkage caused
by structural differences. Spiral or interlocked grain is commonly
responsible. Minor defects of this class may result from uneven
drying, which also can aggravate those due to the wood structure.
Preventive measures are confined to decreasing the rate of drying
and to the use of piling methods which will hold the stock firmly in
place and in proper alignment.
LOOSENING OF KNOTS
Knots are loosened during seasoning as a result of the drying
out of the cementing resins and gums and of differences in the
shrinkage of the knots and the surrounding wood. In a plain-sawed
board, the axis of the knot being at right angles to that of the tree,
the knot shrinks away from the wood lengthwise of the board but
does not do so appreciably in the direction of the board width. As
shrinkage in the thickness of the board is greater than that along the
axis of the knot, many knots are loosened when stock is machined.
The loosening of knots can not be entirely avoided by any method
of seasoning, since a certain type of knot is not directly connected
ee
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER iil
with the wood surrounding it. Depreciation from this source can
be reduced somewhat in air seasoning by measures which prevent
_ excessively rapid drying and extremely low final moisture content.
BLUE STAIN >
Blue stain does not materially affect the strength properties of
wood. It is not an early stage of decay. It does, however,
lower the value of the product for uses in which discolorations
are objectionable or in which the wood is to receive a natural finish.
In the air seasoning of western yellow pine, western white pine,
and sugar pine, the prevention of blue stain is often the major drying
problem.
The blue-stain organism does not attack the living tree, and in
wood products the blued areas are confined to the sapwood, ending
where the heartwood begins. Apparently, conditions favorable
for the development of the fungi are limited to sapwood stock con-
taining a_ suitable
amount of moisture.
The fact that some
species of wood blue
more readily than
others has not been
explained. Possibly
the food or moisture
conditions in the sap
of different woods
vary sufficiently to
account for this selec-
tive action.
Blue stain in its
early development
appears as spots or
streaks. Later, asthe
fungus penetrates
more deeply, the en-
tire sapwood may be ee threads (B) of a blue-stain’ fungus in se
. pine decomposing e medullary rays a ana penetratin
dascoloreds:)Ehede+i! the cell walls at C and D :
fect is a discoloration
of the stock due directly to the growth within the wood of minute
threads of the blue-stain fungi. These fungi are very small plants
which absorb their nourishment from the wood they inhabit, feeding
principally upon the cell contents. As the fungus threads grow, they
pass from one cell to another, usually through the thin parts of the
cell wall but occasionally boring through the wood fiber. The blue-
gray color appears only after these numerous small threads have
reached a certain stage of development within the wood cells. (Figs.
2 and 3.)
Later on, when these threads feeding on the contents of the cell
and to a slight extent on the cell walls have developed further, fruit-
ing bodies comparable in some ways to the flowering part of a green
5 Acknowledgment is made by the authors to E. E. Hubert, formerly assistant patholo-
gist, Bureau of Plant Industry, who has contributed so materially to the present knowledge
of the blue-stain fungi, for the material presented in this section, i
12 DEPARTMENT BULLETIN 1425, U.S. DEPT. OF AGRICULTURE
plant are produced upon the surface of the wood. (Fig. 4.) These
fruiting bodies, resembling small black hairs or bristles swollen at
the base, A, appear as tiny black specks upon the blued wood. From
them, minute spores, B, are ejected which, when carried about by the
wind or other means, cause new infections by germinating on bright
lumber green from the saw or on other favorable places.
Although the blue-stain organism may be present in certain logs
before these are sawed into lumber, the chief source of infection is
the fresh spores. Accordingly yard sanitation, including avoidance
of the too frequent use of crossers, is highly important in blue-stain
prevention.
The conditions for rapid development of blue stain are essentially
the same as for the development of true wood-destroying fungi. Both
require an abundant food supply, a comparatively high moisture con-
tent of the wood, and warm weather. Staining 1s always severe dur-
ing rainy periods in the warmer seasons of the year when the air 1s
humid and seasoning is corre-
spondingly slow. Under such
conditions, if proper piling and
storage methods are not em-
ployed, very heavy staining
may occur, particularly in
fresh-cut stock.
It has been observed that
these fungi grow best on sub-
stances which contain some
acid, the acid of sour sap being
very favorable for the develop-
ment of the blue-stain organ-
ism. This explains why “ sour-
ing” or “fermenting” of the
sapwood is een as
at the origin of the blue-stain
ance ood Wee cr Wien katie wanes Hiemich ae than the true
the direct penetration of the cell walls. In
the lower center one thread is passing cause, fungus development.
through a bordered pit. It is the presence 4 1 1 j
of such threads within the cells that gives From the Investigative work
the blue color to the wood on the moisture requirements
of the blue-stain organism
thus far attempted, it seems safe to assume that there is little danger
of sap-stain development in wood with a moisture content of 20 per
cent or lower. In air seasoning the occurrence of this defect is
primarily the result of insanitary yard conditions and slow drying.
Preventive measures include sanitation and yard practice which will
permit rapid drying, especially in the initial stages and in the lower
third of the lumber pile.
Blue stain is the only stain of economic importance in the air sea-
soning of western softwood lumber and is a major problem only in
drying the pines. In view of the general climatic conditions and the
usual drying periods required in the West, decay need not be con-
sidered as an air-seasoning defect. Of course, incipient infections of
decay that may cause trouble with the stock in later use should be
guarded against, but any of the measures taken to reduce blue-stain
development are also helpful in preventing decay.
a
ve
a
ee
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 13
AIR-SEASONING PRACTICE
THE DRYING YARD
SITE SELECTION
The location of a yard site is largely controlled by such necessary
considerations as timber supply and transportation facilities, and
generally climatic conditions have little weight. But when these
larger considerations have determined the approximate location,
then elevation, topography, surface, and drainage should be taken
into account in the choice of the actual site. (PI. 1.)
Marked differences in elevation, even within a rather limited area,
make a difference in the extremes of temperature and humidity.
Fie. 4.—A, the flask-shaped fruiting body of a blue-stain fungus; B, the
minute spores ejected from the tip of the fruiting body, and capable of
germinating and starting new infections
Topographical features may materially influence the direction and
volume of wind movement as well as the amount of direct sunlight
which reaches the yard each day, thus playing a very direct part in
drying and also exerting an indirect influence on the rapidity with
which the soil dries after rains, the snow melts, and the fog clears
away.
The slope and regularity of the ground have an important bearing
on surface drainage, on proper construction of pile foundations, and
on yard transportation. Poor drainage in the lumber yard is defi-
nitely a contributory cause of slow drying, particularly in those
periods of the year when more rapid drying is most desirable. It
may also hinder transportation and other operations in the yard.
14. DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
The relation of drainage to effective air seasoning is seldom fully
recognized. It is the one natural influence subject to absolute control
in existing yards and should receive more attention than is usually
accorded it.
YARD LAYOUT
Economy or yard space is, of course, a consideration in laying out
the drying yard. It is of greatest importance where land values are
high or the area available is actually limited in extent. But economy
in this respect 1s generally questionable if serious seasoning defects
result. ‘The most rapid drying consistent with the least depreciation
of stock is a primary objective of air seasoning.
The layout of the drying yard should therefore depend in a large
measure upon the climatic conditions to be encountered. If tem-
perature, humidity, and wind movement are of such character that
slow drying may be expected, the yard should be laid out in a much
more open manner than would be necessary with rapid drying. In
the fog belt of the Dougias fir region, for example, congestion in the
drying yard is a more serious difficulty than in the San Joaquin
Valley of California.
MAIN ALLEYS
In planning the drying yard the direction and width of the main
alleys should first be decided. ‘These alleys must accommodate all
the transportation and handling of lumber in the yard, of course,
but, if seasoning is to be properly done, they must also function as
well-defined channels of air circulation in the yard and of sunlight to
the front of the lumber piles. The operating functions must be con-
sidered, but it is the drying functions that are of major importance.
Only too often convenience in handling is given undue weight in the
yard plans.
Of the three things that may influence the layout of the main
alleys, slope may be of special importance because it affects con-
siderably the transportation system, particularly that of the gravity
type. But direction of prevailing winds and the desirability of
maximum direct sunlight against the piles and on the alley floor
bear directly on the seasoning problem and should be of chief
concern.
The desirability of admitting heat from the sun’s rays to as much
of the pile as possible has been emphasized. ‘This can best be accom-
plished by a north-to-south arrangement, for it permits the direct
rays of the sun to strike farther down on the pile, front and back,
for a longer period of the day than will an east-to-west arrangement.
The transmission of more heat to the sides of the pile in an east-to-
west arrangement does not equalize this advantage, because of the
narrow spacing inevitable between piles on the same alley. The
benefit in north-south alleys is most pronounced in the cooler and
wetter months, when it is most needed.
The main alleys offer the best channels for the movement of air
currents in the yard. Thus it is apparent that their alignment
parallel to the direction of the prevailing winds would be favorable
to yard circulation. But in spite of this advantage their location
from north to south, irrespective of prevailing wind direction, will
probably give the best drying conditions.
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 15
Drying conditions surrounding the lumber pile are improved by
the north-and-south alley in the seasons of greatest humidity. Snow
does not accumulate as rapidly or remain as late in the spring at
the front or rear of the piles. Fog is cleared with less delay.
Even if the prevailing winds come from the east or west, their
effect on yard circulation need not be lost if the narrow spacing
between the sides of the piles is made continuous from alley to alley
across the entire yard.
_ Apparently little thought has been given to direction of layout
in the construction of most western yards. Both north-south and
east-west arrangements are found very generally in the several pro-
ducing regions. In the building of new plants and the extension of
existing yards, the definite merits of north-and-south alleys should
be given recognition. The decision as to the direction of the main
alleys will of course settle as well the direction of the other openings
in the yard.
Main alleys are seldom so narrow as to restrict unduly either lum-
ber handling or the movement of air currents in the yard, and yet
the maximum drying benefits from the direct rays of the sun are not
to be obtained with a minimum width of less than 16 feet. ‘The
width should preferably be 20 feet, especially where drying is natu-
rally slow. ‘“hroughout the West, main alleys are commonly 16 to
18 feet wide but range from 12 to 26 feet. (Pl. 2, A.) Strangely,
the narrower alleys are usually found in yards where general sea-
soning conditions would dictate the maximum.
REAR ALLEYS
Rear alleys are sometimes utilized for lumber handling, but their
real function is to improve drying conditions. Their effectiveness is
dependent, as is that of the main alleys, upon direction and width.
In view of the very general necessity for economy of yard space, a
width of 12 feet is recommended. However, where rapid drying is
sought, rear alleys 16 feet wide are more effective. If an extremely
open layout is essential, the rear alleys should bear a greater propor-
tion of the increase in width than the main alleys. The need for sur-
face improvements in the main alley, which must be suitable for
transportation, ordinarily prohibits a width of more than 20 feet.
In western softwood yards rear alleys 8 to 12 feet wide are very
common, but variations from 2 to 80 feet are found. ‘That the sea-
soning benefits from adequate spacing are not fully appreciated is
evident in the use of narrow rear alleys in some of the locations most
unfavorable for drying.
CROSS ALLEYS
Cross alleys, openings at right angles to the main alleys, serve a
number of purposes. They reduce the fire hazard, facilitate trans-
portation and general movement about the yard, and influence the air
circulation. Local conditions naturally have an important bearing
on the interval between cross alleys. An ideal arrangement, which
some yards boast, is a cross alley every 200 to 300 feet, although this
is not always practicable. In the average yard there should at least
be 8 or 10 with a minimum width of 20 feet. Sixty feet is very de-
16 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
sirable in the interests of fire protection. The great variation found
in existing yards indicates a failure to appreciate the value of cross
alleys. Some yards 2,000 feet in length have none.
SPACING BETWEEN PILES
The necessity for proper spacing between the piles on the same
alley can not be emphasized too forcibly. The primary purpose
of these openings is to aid air circulation, not only to supplement
the alleys in building up general air currents in the yard, but also
to exert a very definite effect on the horizontal circulation in the
lumber pile. The front and usually the rear of a pile, because of
the location of the crossers, present an almost solid face. The sides
of the pile offer the only easy inlet and outlet for downward air
currents. A very definite circulation along the sides of the pile
is essential to effective drying. To obtain this, a spacing of at least
3 feet and preferably 4 feet should be used. Where local air move-
ment is sluggish, a spacing of 5 or 6 feet may be justified. A second-
ary benefit from adequate pile spacing is that as the width is
increased the direct rays of the sun strike farther along the sides
of the pile during a greater part of the day.
If the relation of adequate pile spacing to the air-seasoning process
is appreciated by the lumber industry of the West, it is not apparent
in present practice. Although a maximum spacing of 6 feet is
occasionally used, the average is about 2 feet, and many yards have
still narrower spacing. In certain yards where slow drying and
the resultant difficulties exist, the most effective single improvement
would be to widen materially the spacing between the sides of the
iles. |
7 In order to cbtain the maximum benefit from local wind currents,
the openings between the sides of the piles should be continuous
from alley to alley, providing unbroken channels from one side of
the yard to the other. (Pl. 2, B.) This arrangement is especially
desirable where the prevailing winds come from the east or west
and the main alleys are laid out from north to south. To effect
this arrangement it is necessary to segregate stock lengths in the
yard by blocks rather than by alleys unless a uniform width of pile
foundation is used throughout.
The advantage of this type of layout is recognized to some extent.
Tt is commonly found in the California pine region and occasionally
in the Inland Empire and Douglas fir regions. Oddly, in the red-
wood region, where climatic conditions make for generally slow
drying, this arrangement is not in use.
TRAMS
The use of trams in the drying yard should be discussed in connec-
tion with layout, for where the ground is very uneven trams may
seem desirable for facilitating yard transportation. Also, higher
piles can be erected by hand in tram yards. But the hindrances to
seasoning inherent in trams may more than offset their benefits. Air
movement below the level of the tramways is seriously retarded, just
where it is of greatest importance in order to maintain a positive
ee
a Se ee ee —
—* LSS Se ee
PLATE?
1425, U. S. Dept. of Agriculture
Dept. Bul.
GHVA ONINOSVAS-YIV NYSALSAM V
PLATE 2
Dept. Bul. 1425, U. S. Dept. of Agriculture
SepIs 9y} 18 Seid U9eMI0q SUloVvds JUsT[V0x y—’ {
pred ay sejsnoq 4dey-[[omM url AoT[e ureur [BoIdAY W— V
YSdEINNT GOOMLAOS AO ONINOSVAS YIV NI S0ILOVdd GOOD
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER vs
horizontal circulation in the lower part of the pile. Tramways also
prevent the direct sunlight from reaching the lower part of the pile.
Naturally, the rate of drying below the tram level is greatly
affected. Actual yard tests under ordinary conditions have shown
that stock below the tramway requires 40 per cent more time to dry
down to a given moisture content than stock above the tramway.
Also, during a given period, stock below the tramway will reach a
moisture content of only 18 per cent while the stock higher up is
coming down to a moisture content of 11 per cent. It follows that,
in drying pine, stain development is much greater below the tram.
Such differences between the upper and lower part of the pile are
very much greater than in piles of the same height where trams are
not used.
Trams are going into disuse gradually but surely. A considerable
number of tram yards are still found in the California pine region,
but only an occasional one is found in the Douglas fir region; there
are few in the Inland Empire and in the redwood region. Where
trams are in use, their effect on drying should be definitely recognized
and circulation below the tramway assisted as far as possible by
modifying the arrangement of the lower part of the pile.
PILE FOUNDATIONS
The foundation upon which the pile is erected should be so con-
structed as to perform several very definite functions, the least of
which are the designation of the location of the pile and the keeping
of stock from direct contact with the soil, for almost any kind of
bottom will do these things. Horizontal algnment of the lumber, to
prevent deformation and even breakage in the lower part of the pile,
depends largely upon the foundation. Construction must therefore
be such as to prevent appreciable sag at any point. To provide ade-
quate bearing surface for the stock, a stringer must be placed across
the width of the foundation for each tier of crossers to be used in
piling. But the function of vital importance to seasoning, and the
one generally disregarded, is the facilitating of proper circulation.
Adequate clearance between the ground and the foundation string-
ers is necessary for both horizontal and vertical circulation. It is
absolutely necessary for positive horizontal circulation at or near
the bottom of the pile, by which means the moist air dropping to the
bottom of the pile is removed. Not only does such construction
provide for the flow of moist air from beneath the pile, but also it
affords access to wind currents from the main and rear alleys. These
currents find little if any ingress at the front and back of the pile
because of the crossers,
TYPES OF FOUNDATION AND STRUCTURE
Plates 3 and 4, illustrating the standard types of the better foun-
dations now used in the West, show the basis for recommendations.
The construction shown in Plate 3, A is an example of the unit pier
and stringer bottom. Plate 3, B shows the common pier and stringer
foundation of the continuous type. Both of these are excellent if the
ground is properly prepared and heavy mud sills are used. The
109391°—28——-3
18 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
unit type is cheaper to construct, more easily kept in repair, and, if
the yard is properly laid out, assures adequate and uniform spacing
of the piles. It is generally more flexible than the continuous type,
as it can easily be changed to accommodate different lengths of stock
and to make repairs.
Another style of foundation, which has much merit, is illustrated
by Plate 4, A. It is the most rigid type in use and definitely pre-
cludes any variations in the spacing between the sides of the piles
when once the yard is built. One admirable feature is that the
stringers upon which the lumber is piled are not attached to the
permanent part of the structure, but can be moved to support stock
of different lengths. This type assures a firm bearing at each tier
of crossers. Obviously, much better original material and a higher
labor cost are required than for the other two types. Also, because of
the cross and lengthwise bracing, more obstruction is offered to air
movement under the pile. In Plate 4, B is shown a good type of
pile-bent foundation, necessary where the yard is located over water.
These examples of construction are above the average for the
western softwood territory generally. Very poor foundation con-
struction is too often found. Local conditions will affect the choice
of structure, but whatever type is preferred the chief functions of the
foundation should always be clearly kept in mind. The use of con-
crete piers or treated wood supports for the foundation stringers
has much merit. Moist air and damp soil beneath the lumber pile
are naturally favorable to decay, and untreated members in contact
with the soil require constant replacement if poor alignment is to
be avoided.
NUMBER OF FOUNDATION STRINGERS
In general, a stringer should be provided for each tier of crossers
in the piled stock. The number of crossers that should be used to
each course of the lumber will be covered later under “ Pile construc-
tion,” but as a broad principle it may be stated here that for western
softwoods the maximum distance between supports should be 8 feet.
In order that different stock lengths may be provided for, the type of
bottom shown in Plate 4, A is very desirable as being the most fiexible
in this respect. With other types, special foundation must be pro-
vided for different length piles. Plate 4, C illustrates the effect of
insufficient bearing.
HEIGHT OF FOUNDATION
Actual study has shown that adequate unobstructed clearance be-
neath the lumber pile is a basic factor in effective air seasoning.
Controlled yard tests have demonstrated that as the foundation
height is increased the inherent lag in drying between vertical sec-
tions of the pile is decreased; final moisture content of the stock is
more uniform throughout the pile and during a given period will
reach a lower average; and, in pine, depreciation from stain is re-
duced, particularly in the lower third of the pile where blue-stain
development is ordinarily greatest. In drying redwood, a difference
of 12 inches in the rear height of the foundation resulted in a final
average moisture content of 18 per cent for the stock on the higher
bottom and of 12 per cent for that on the lower. Stock in the higher
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 19
pile reached an average moisture content of 23 per cent in 128 days,
whereas that is the lower pile required 191 days, or a period half
again as long, to come down to 23 per cent.
Increase in the foundation height is justified up to the point where
the loss of yard space and additional cost of piling may offset the
very real seasoning advantages mentioned. The minimum clearance
below the stringers upon which the stock rests should be 12 inches.
This means ordinarily a foundation height of 18 inches at the rear,
and proportionately more at the front if the usual slope is built into
the structure. When the influence of an active horizontal circulation
under the pile is correlated with the local seasoning problem, a
greater clearance may be found profitable. In yards where the rate
of drying is exceptionally slow, an 18-inch rear clearance may be the
most effective and cheapest remedy, returning real dividends on the
added cost. Further, this potent aid to fast drying can never be the
cause of depreciation from excessive drying, since it affects primarily
only the lower section of the pile.
In practice to-day the average rear height of foundations is be-
tween 8 and 12 inches, which at best means a clearance under the
pile of about 6 inches. Practice varies, however, from a 4-inch
height—simply stringers laid on the ground—to 24 inches, or a
rear clearance of 18 inches. Plate 5, A shows an only too common
type of foundation. With such construction, wind currents along
the alleys exert but little effect upon the circulation under the pile.
It is not difficult to appreciate how damp and sluggish the air must
be in the lower portion of these piles and beneath them.
SLOPE OF FOUNDATION
The slope in the foundation from front to rear is many times
given more thought than other more essential considerations. A
slope of from 0.5 to 1 inch per foot of length is commonly used.
This, if carried up in part at least with the pile, undoubtedly makes
it easier to give adequate pitch to the roof and consequently to se-
eure good run-off. Also, water leaking into the pile will drain off
more rapidly. With the piles adequately roofed, however, slope be-
comes of minor importance, except as it may be of some little
mechanical assistance in constructing the pile. If slope is not built
into the foundations, it may be obtained by using extra crossers
at the front and center, as illustrated in Plate 3, A.
DIRECTION OF FOUNDATIONS
Almost without exception in the West, lumber is piled perpen-
dicularly to the alleys, and foundations are constructed accordingly.
Piling parallel to the alleys has sometimes been considered to be a
superior means of seasoning, but this claim was not substantiated
when actual comparisons of the two methods were made. Two very
apparent objections to parallel piling are, (1) that the run-off
from the roof falls in the narrow spacing between piles, where the
soil necessarily dries out more slowly than in the wider rear alleys;
and (2) that the cost of handling stock by this method is greater than
by perpendicular piling.
20 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
GENERAL YARD CONDITIONS
Plates 2, A and 4, C offer a remarkable contrast of sanitary condi-
tions as actually found in the West. There is much room for im-
provement in most of the yards. No yards have been seen where
recommendations for sanitation have been taken too literally or
overdone. The cleanliness of a yard is largely a matter of habit
with the workmen, and therefore the prevention of débris accumu-
lation should be definitely insisted upon. Incidentally, cleanliness
and order about the yard inevitably inspire the employees with more
pride in their work and result in greater efficiency.
Weeds and other vegetation in the drying yard not only retard
air movement under the piles but also decrease the rate at which
the ground dries after rains. How unfavorable both of these effects
may be can be visualized by referring to Plate 5, B, particularly if
this view is compared with the admirable conditions shown in Plate
9, A. Excessive vegetative growth in the yard should be prevented,
and this may be accomplished in a number of ways. Chemical weed
killers or sheep grazing may supplement or entirely do away with
the more costly and less effective use of the scythe.
Methods of handling and sorting crossers not in use may also ©
have an important bearing on seasoning. It is not unusual to find —
the circulation under a green lumber pile entirely or partially 7
blocked by crossers and roof boards which have been thrown or ~
stacked on the ground against the front, rear, or sides of the founda- —
tion. Plate 4, A illustrates a practice which greatly reduces this
evil. The extension at the front of the foundation provides a con- —
venient place for roof boards, and cross pieces between the sides of —
adjacent foundations afford similar storage for crossers. With such —
practice, none of this material left after the erection of a new pile
will be lying about to stop circulation beneath the foundation. 7
Methods of this kind tend also to prevent breakage and warping ©
and to keep crossers off the ground and consequently drier. Dry
crossers are less lable to become infected with blue stain and to
transmit the stain to the stock piled upon them.
Yard sanitation is a very practical measure in the control of blue
stain. It has already been stated that the principal source of blue-
stain infection is in the spores produced when the fungi have de-
veloped sutliciently on piled stock or other suitable material. Incipi- —
ent infection of decay is caused in the same manner. Preventive
measures are quite logically aimed at attempting to avoid the condi- ©
tions favorable to growth of blue stain; but the lability of infection —
should also be reduced as far as practicable. Mull refuse should ~
never be placed in the yard, and broken boards and like débris should ~
not be allowed to accumulate. Such material, in addition to increas- —
ing the fire risk, is soon infected with stain and decay organisms and ©
rapidly becomes a new source of infection. |
YARD TRANSPORTATION
As would naturally be expected over such a large territory as the ©
western lumber-producing region, numerous and varied methods for ©
the movement of lumber to and from the drying yard are employed. ©
Transportation over a track system by either motors or horses is
a ee 3
Dept. Bul. 1425, U. S. Dept. of Agriculture PLATE 3
et
ul HA Minin
t
tt
-
o.- eee
Bie et oe ee
TWO VERY SATISFACTORY TYPES OF FOUNDATION
A.—The unit pier and stringer foundation
B.—Continuous pier and stringer
Dept. Bul. 1425, U. S. Dept. of Agriculture PLATE 4
GOOD AND BAD FOUNDATIONS
A.—A well-constructed rigid type
B.—Pile-bent foundation over water
C.—A poor foundation in an insanitary yard
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 21
common, particularly in yards of large area. Both gas and electric
surtace carriers, which actually carry the lumber rather than merely
haul it, are gaining in popularity. Auto trucks, especially con-
structed to permit automatic loading at the green chain and unload-
ing upon scaffolds or sawhorses at destination are also used.
Wagons and dollies propelled by tractors or horses are still employed
to a considerable extent, and a new development, rather limited as
yet, is the use of monorails or cranes in the yard.
Such a wide range of methods is in some measure attributable to
differences in local conditions. Topography, surface conditions, size
and layout of the yard, species and sizes of stock, and similar ele-
ments may have an influence upon the type of transportation selected.
These must necessarily be correlated with such factors as cost of
actual moving operations, effect of the transportation system upon
the efficiency of related yard operations, and influence of the system
upon seasoning conditions. It is not within the scope of this bul-
letin to attempt a full discussion of the many and complicated phases
of .efficient yard transportation. However, some reference to its
relation to other yard operations and to seasoning conditions is
pertinent.
The relation to other yard operations can be well illustrated by
some comparisons between two very different types of transporta-
tion. The use of wagons and horses in the yard is a most inflexible
method. Stock must immediately be unloaded by dropping it on
the ground. If not in the proper location for piling, it is difficult
and costly to move. When hand piled, one-third to one-half of
the lumber in each pile must be handled twice, once on to scaffolds
and once on to the pile. Despite care in unloading, the stock comes
in contact with dust and mud. During the dry season dust raised
by the teams penetrates the piles. Dirt and grit thus accumulating
on the lumber not only increase the liability of blue-stain infection
but later have an appreciable effect on planer knives.
The track system, on the other hand, is a most flexible method of
transportation. Stock can be held on the trucks until piled, allow-
ing temporary storage, when necessary, in any part of the yard and
avoiding congested working conditions in the alleys. Stored trucks
can later be moved easily to the final location. Since the loads are
high and conveniently moved, and all piling can be done directly
from the trucks, work on one high and one low pile can be carried
on at the same time. The stock never comes in contact with the
ground; dust is of little consequence in tracked yards; and the
lumber handlers lose no time waiting for teamsters.
The movement of lumber to and from the drying yard is often
considered merely as a physical operation, without its being realized
that the transportation method employed may materially influence
seasoning. The direction of the yard alleys may be fixed by the
transportation system rather than by seasoning considerations.
Transportation by certain methods can very materially add to depre-
clation losses through incidental breakage and damage. The influ-
ence of these methods upon the height of hand piling may result
in congested yard conditions, in low foundations, and poor piling
practice. Some methods of transportation can definitely increase
the liability of stain infection in pine yards.
92 DEPARTMENT BULLETIN 1425, U.S. DEPT, OF AGRICULTURE
SEGREGATION OF STOCK FOR PILING
The sorting of green lumber by species, grades, and sizes follows
to some extent a general standard in each region. It is of necessity,
however, primarily an individual plant problem because of the many
considerations involved. Quantity production of different items,
sorting and yarding facilities available, trade customs and demands,
and requirements for proper seasoning must each be considered in
its proper relation to the others. Of these, the items produced in
quantity and the yard facilities ordinarily vary most as between
plants. Seasoning requirements, although of real moment, are rarely
given their proper weight in the choice of a sorting practice.
IMPORTANCE IN AIR SEASONING
Proper stock segregation is an essential element of effective air-
seasoning practice. Individual species usually have distinct drying
requirements and accordingly should be piled separately. This is
also largely true for different grades of the same wood, although
some of these may be segregated for drying by natural groups. The
soundness of such methods can best be demonstrated by a specific
example. :
Western yellow pine and white fir, species commonly produced at
the same plant, need very different seasoning treatment. Western
yellow pine is more susceptible to blue-stain depreciation than any
other western species and therefore requires a method of pile con-
struction which will favor fast drying and thus tend to retard
development of the stain organism. White fir, on the other hand,
is not subject to stain depreciation but is much more liable to check
if seasoned rapidly. In the select grades of western yellow pine
sapwood is present to a greater extent than in the common grades,
and the select grades are therefore more susceptible to blue stain.
~The common grades, however, because of greater hability to knot
defects, call for slower drying.
Segregation of stock by thickness is almost a necessity because of
the difficulties incident to piling the unsorted lumber. With lumber
of random thickness it is practically impossible to obtain an even
bearing surface for the crossers and thus to avoid warped stock and
poor horizontal circulation. Another serious objection is that the
drying period for the entire pile is dependent upon the time required
by the thickest pieces. For example, 4/4 stock requires but 50 to 80
per cent of the time necessary for 8/4 stock to reach the air-dry con-
dition, the ratio varying with different species, grades, seasons of
years, and general drying conditions.
For thorough seasoning, width segregation is of real value. The
vertical air circulation in the lumber pile should be assisted in every
way practicable by the method of pile construction. Unobstructed
vertical channels throughout the width of the pile are therefore very
desirable, and it is only by piling separate widths that uniform verti-
cal flues extending from top to bottom of the pile between each tier
of boards are possible.
Segregated lengths are also an advantage in piling for air season-
ing. With each length separated it is more readily possible to em-
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 23
ploy the box type of piling, which, as will be pointed out in the dis-
cussion of pile construction, is considered extremely desirable.
Random lengths can be box-piled but only with more difficulty.
CURRENT PRACTICE
Although regional standards differ and the problem is definitely
affected by local plant cenditions, the principles followed rather
generally in the West are of interest. Species are almost always
segregated. It is also fairly standard practice to separate grades—
at least by groups, such as selects, shops, and common. Common
particularly is generally sorted by individual grades. Each thick-
ness is piled by itself. Inch selects are commonly separated by
widths, while thicker selects and most shop are handled in random
widths. No. 3 and better common is ordinarily segregated by
width, and the lower grades of common are occasionally sorted in
that manner. The sorting of lengths is the practice least consistently
followed. At the more progressive plants, however, particularly
those of large daily production, a great deal of lumber is piled in
separate lengths. Shop lumber is very generally handled in random
lengths.
Thick select and shop lumber is piled random width primarily
because of trade requirements, although volume production is also
a factor at some plants. The handling of the lower grades of
common in mixed widths is due to the low value of the product and
to the customary method of selling in all-width lots. The less
desirable size segregation of other stock is usually the result of
inadequate sorting facilities or small production.
in spite of limitations of space and production, a greater amount
of stock can be piled in separate widths and lengths if less segre-
eating of grades is done. Although the piling of separate grades
is often desirable from an operating standpoint, that is not always
rightly the major consideration. Grade and size segregation
should be balanced one against the other in the light of the season-
ing as well as the operating advantages. Too often the more tangible
operating advantage is allowed to predominate in the decision and
the actual dollars and cents savings from improved seasoning prac-
tice are overlooked merely because they are less easily recognized.
PILE CONSTRUCTION
MAJOR CONSIDERATIONS
Two distinct major considerations are involved in the logical
development of methods of pile construction—losses to be avoided
through proper seasoning and economy in piling cost and yard
space. Here again intangibles and tangibles are in conflict, and
the advantages of one must be weighed against those of the other.
‘It is because of the lack of a sure basis for judgment in such decisions
that true efficiency in air seasoning is so generally defeated.
A reduction in operating expense is apparent not only upon incep-
‘tion but with each monthly and annual cost statement. The depre-
ciation losses that result directly from poor seasoning conditions are
easily overlooked and are rarely accurately inventoried. And yet
94. DEPARTMENT BULLETIN 1425, U. S. DEPT, CF AGRICULTURE
a reasonable addition to the piling cost may readily pay for itself
many times over by a considerable saving effected through reduction
of degrade. More rapid stock turnover, lower shipping weights, and
the customer’s appreciation of low, uniform moisture content are
also actual returns from what may appear to be more costly piling
methods.
Of course, climatic conditions must serve as a guide to piling
practice. To illustrate, during the active drying season in the Inland
Empire hot days with extremely low humidity are common. In the
redwood region a greater humidity is the rule. The method of pile
construction used in the Inland Empire must anticipate deprecia-
tion from checking to a greater degree than would be needful in
the redwood region. Again, high piles are more practicable in a
warm climate than in one less favorable to drying, for in the warm
climate the amount of direct sunlight which reaches the lumber pile
is less important.
The layout of the drying yard also bears on the methods of piling
to be followed. Stain development is a more acute problem of pile
construction in a crowded yard than in a less congested one. If
trams are employed, slow drying and the incident evils occur in the
stock below the tram level. Under such conditions more expensive
pile construction is justified to build up the air circulation in the
lower part of the pile. |
It has been pointed out that, because of their different degrees of
susceptibility to defect, different species need individual treatment.
Similarly, the several grade groups of the same wood may require
different pile construction, not only because of differences in defect
development but also because the greater the value of the product
the greater the expense justified to prevent depreciation. Thickness
of the stock, since it affects the rate of seasoning and liability of
depreciation, also necessitates adaptations in piling,
TYPE AND SIZE OF PILES
Three general types of lumber piles are used in western softwood
yards. The so-called box pile is commonly employed in all of the
producing region. Plate 5, C, is a rear view of excellent box piles.
What may be termed a “ modified box ” pile is shown in Plate 5, D.
This type is used very generally in the Douglas fir region but is not
common elsewhere. <A third type, and one that is found in too many
yards in each region, may be called the “random length” pile. This
method of piling, which is illustrated in Plate 6, A, is obviously an
improper one for efficient air seasoning,
THE BOX PILH
Box piling is a method that permits the ends of the stock to bear
upon the front and rear crossers, which should in turn bear directly
upon the front and rear foundation stringers. Expressed another
way, the stock does not overhang the rear crosser. This method has
real advantages. Both segregated and random-length lumber can
be piled in this manner. Stock is uniformly protected from the
weather and all parts of the lumber are given adequate bearing sur-
|
;
:
|
.
Dept. Bul. 1425, U. S. Dept. of Agriculture PLATE 5
MY
\“
TYPES OF FOUNDATIONS AND OF PILING
A and B illustrate foundations and yard conditions that should never be permitted in softwood
yards
C and D show types of piling that are very satisfactory when carefully done. C.—Box piles,
rear view. D.—Modified box piling
Dept. Bul. 1425, U. S. Dept. of Agriculture
PLATE 6
A.—The random-length type of pile
B.—Common pile stock crossers 1X12 inches, 16 feet long.
Crosser-stain has developed in Nos. 2 and 3
Season check shows in Nos. 1 and 4.
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 25
face. Considering all kinds of stock and all kinds of weather condi-
tions, the box pile will undoubtedly give best seasoning results.
Random-length lumber is usually box piled by placing one end of
the short pieces alternately on the front and rear crosser. This
practice tends to allow the crossers to “ weave ” somewhat and may
result in considerable depreciation of the crossers and to some extent
of the stock. This may, however, be avoided with little, if any,
additional expense. The usual run of even-width stock, 10 to 16
feet in length, contains at least 50 per cent of the latter length. By
carrying up the two outside tiers of boards and from three to five
interior ones, depending upon the width of the stock, with 16-foot
boards, the rear crossers are given adequate bearing surface even
though all of the shorter pieces be placed flush with the front of
the pile. This permits a good box pile, but lengths longer than 16
feet must be piled separately.
The criticism of the box pile is sometimes made that there is
greater liability of end checking than if 2 feet or more of the stock
overhangs the rear crosser. The theory is that this overhang allows
an equalization of the stresses caused by the uneven shrinkage which
results from the more rapid drying of the end grain. But with
proper methods of box piling end checking need not be appreciable.
If the front and rear crossers are permitted to project beyond the
ends of the stock, these ends are shaded from direct sunlight and
the rate of end drying is reduced. Narrow crossers should also be
used to reduce the area of the stock not exposed to the air. With
these methods, which are covered fully in the later discussion of
crossers, the end checking incident to box piling is not to be com-
pared with the depreciation which occurs in the overhanging ends
of the random-length pile. Such a conclusion is substantiated by
the opinion of representative Jumbermen, observation at numerous
plants, and the results of specific studies.
THE MODIFIED BOX PILE
The modified box pile is limited in use to separate-length stock
and differs from the box type in one other particular. The rear
crosser is placed 18 to 24 inches back from the ends of the stock.
With the rear of the pile presenting a solid regular face and a
maximum overhang of 2 feet, this type is far superior to the
random-length pile. It offers greater protection to the overhanging
ends from the weather extremes and does not permit as much de-
formation. The lability to end checking is probably less than in
careless box piling where wide stock is crossed with itself and the
crossers do not project beyond the ends of stock. The modified box
type is well adapted to seasoning even-length stock in regions where
low humidities and excessive drying do not occur at any season of
the year. This is particularly true with stock thicker than 4/4
- and with the lower grades of common in which a certain amount
of checking and slight deformation is permitted.
THE RANDOM-LENGTH PILE
There is entirely too much use made of the random-length pile in
the western softwood regions. The varied-length overhang at the
109391°—28——_4
26 DEPARTMENT BULLETIN 1425, U. 8S. DEPT. OF AGRICULTURE
rear of the pile (pl. 6, A) can only result in depreciation of one
kind or another. Exposed to the direct rays of the sun and the other
weather elements the overhanging ends are subjected not only to
excessively rapid drying but usually to alternate wettings and dry-
ings. Also, there are no supports to hold these ends in alignment
during seasoning. As a consequence, end checks, splits, warp, twist,
and cup occur. Use of this type of pile can be justified only with
products of very low value and which permit large amounts of the
defects mentioned. Such stock would include No. 5 boards, culls,
shims, and similar material.
PILE WIDTH
Width of the lumber pile is ordinarily determined by other details
than a consideration of its effect upon drying conditions. The width
of foundations, the method of crossing the stock, and the plan of
stock segregation usually influence this matter. If unit foundations
are 16 feet wide, piles are this width. With separate provisions for
each length of stock, the foundations are ordinarily square, and pile
widths correspond. Square piles are also used where stock crossers
are employed on separate-length stock. With random lengths, the
longest piece often controls the width of the pile. When 18-foot and
longer stock is piled separately, however, the piles are commonly
only 8 to 12 feet wide, owing to the relatively small production of
such sizes and the necessity for smaller piles.
Although varying greatly at individual plants, pile widths as a
rule follow a general standard in each region. The unit foundation
is common in the California pine territory, and piles are usually 16
feet wide. This is true to some extent in the Inland Empire, but
there the square pile is employed most frequently. Although pile
bottoms in the redwood region are generally of the continuous type,
pile widths are mostly 16 feet. In the Douglas fir region the square
pile is the standard.
Despite the fact that seasoning considerations are given little
weight in fixing the pile width, this element of pile construction has
an important bearing on drying. Stock at the center of the pile has
been found to dry much more slowly than that near the sides. Natu-
rally this lag becomes smaller as the top of the pile is approached
and is less pronounced during the active drying season. This varia-
tion is clearly shown by Figure 1, which pictures actual drying in
a representative pile 16 feet in width.
With Inland Empire conditions, the average lag in drying between
the center and the sides of the pile is approximately one month in
the lower third of the pile and two weeks in the upper third. Nat-
urally, as the width of the pile is decreased this differential becomes
smaller, and the average drying period for the pile is shorter. Actual
yard tests with sinker redwood stock substantiate this nicely. In
piles 8 feet wide an average moisture content of 19 per cent was
reached in 1386 days. Stock in piles 16 feet wide, put up at the same
time and under exactly the same conditions, came down only to an
average moisture content of 36 per cent during the same period.
The conditions determining the pile width in actual yard practice
are ordinarily of a fixed nature and accordingly difficult and costly to
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER a
change. However, if slow drying is a serious problem, reduction in
the width of the piles must be considered, since it is a very definite
remedy for such a condition. But with the more usual situation,
sluggish drying can be avoided by other and less troublesome modi-
fications in pile construction. As a general proposition square piles
are most desirable for stock 10 to 16 feet in length. Lumber 18 feet
and longer should be seasoned in piles not over 16 feet in width.
Here, not only is the rate of drying involved, but this class of stock
is commonly produced in such small volume that large piles would be
kept open too long.
PILH HEIGHTS
Height of piles probably averages 14 to 18 feet, or 80 to 100 courses
of inch lumber, fairly generally throughout the western country,
although higher and lower piles are customary in certain districts.
Hand piling is limited to about 100 courses in tracked yards and to
80 courses where lumber is piled from the ground. Above these
heights machine pilers or other mechanical methods are necessary.
Ordinarily, when all factors are considered, a maximum pile height
of about 18 feet, or 100 courses of inch lumber, is most desirable.
It is true that, higher piles are more economical of yard space but
very definite disadvantages must be admitted. Average cost of piling
is increased, and a larger depreciation from sphtting and breakage
may occur. Another very important objection is the bad effect of
high piles, as already noted, in shading the lower sections of the piles
and also in increasing the difference in rate of drying between the top
and bottom of the pile. It may be contended that higher piles permit
more stock to season under the more favorable conditions that prevail
in the upper sections, but there is a fallacy in this general assumption.
Although in a single high pile in the yard an increased proportion of
the stock would probably be benefited; in a yard made up of high
piles such an advantage would not be found. The unfavorable drying
conditions both within and adjacent to the piles would not only be
intensified, but their general level would be raised throughout the
yard. With the differential between the rates of drying at top and
bottom increased, the time required to bring all stock to desired mois-
ture content would not be shortened, and the hability of depreciation
from shrinkage defects would be greater, at least during certain
periods of the year.
PILE PITCH
Lumber piles are commonly constructed with a pitch or an incline
toward the alley which results in a gradually accumulating overhang
at the front of the pile. Usually this is shght, but it occasionally
averages an inch to each foot of height. This pitch, which allows
the drip from the front stickers to fall clear of the pile instead of
draining into it, is of much less importance where real roof protec-
tion is provided, permitting plenty of overhang at the front and rear
of the pile. A slight incline toward the alley, in effect just enough
to guard against a backward pitch, is, however, an advantage in the
mechanical operation of piling.
98, DEPARTMENT BULLETIN 1425, U. S. DEPT, OF AGRICULTURE
CROSSERS
The crossers, or strips or boards placed between the courses of
stock at right angles to the stock to facilitate drying, affect not only
the horizontal air circulation in the pile but the horizontal alignment
of the stock as well. The method of crossing employed has a far-
reaching effect upon general pile construction, upon operating costs,
and upon depreciation of both stock and crossers. The crossing or
“ sticking” of lumber is therefore a matter of utmost importance in ~
air seasoning. Solution of many perplexing drying problems will
be found in the adoption of proper methods of crossing. .
NUMBER OF LAYERS OF STOCK TO THE COURSE
Western softwood lumber is very largely piled one layer to the
course, each layer of stock being separated from those above and
below by crossers. Because of its tendency to stain, pine is always
piled in this manner. ‘ Larch-fir,” or western larch and Douglas fir,
which is handled and sold as a single product in the Inland Empire,
is, however, very generally piled two layers to the course and some-
times three. In the same region, white fir, cedar, and spruce are occa-
sionally “ double-decked.” Certain grades of redwodd and the white
fir of the California pine territory are often dried two layers to the
course. Double-decking is also used to a limited extent at some plants
in the Douglas fir region. 7
Apparently the objects in view in double-decking, particularly in
the Douglas fir region and to some extent in the others, are primarily
to increase the capacity of already congested yards and to facilitate
more rapid piling. However, to a considerable degree, the practice
of piling more than one layer to the course is prompted by the desire
to reduce depreciation from the checking and loosening of knots that
occur at times of the year favorable to very rapid drying. Although
the average rate of seasoning is cut down by this means and probably
some forms of degrade are reduced during very brief periods of the
year, this system of piling has very real disadvantages and very
largely defeats its own ends.
The drying time is necessarily increased greatly. Uniformly
dried stock is out of the question, and the uneven drying of the
two faces causes serious depreciation from checking and cupping,
both during and after seasoning. Careful tests have been made to
determine the relative amounts of degrade resulting when the single-
layer method and the double-layer method were used. In white fir,
double-decking resulted in a 75 per cent greater depreciation than
that from single piling—almost entirely due to cup and check. Fur-
ther, double-decking produced, for the same drying period, a mate-
rially higher moisture content. As might be expected, the difference
in degrade is not so pronounced with stock 8 inches or less in width.
Although it must be granted that the seasonal piling of certain
woods by the multiple system may at times actually have some merit,
any unforeseen contradiction of weather conditions, such as a late
wet spring followed by an early dry season, very often precludes
the success anticipated. Everything considered, excessively rapid
drying can be avoided more effectively by other changes in pile
———-
——_ ee eee
4
|
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 29
construction productive not only of slower but of more uniform dry-
ing. These include narrower spacing between boards, thinner stick-
ers, and other methods to be discussed later.
FLAT-PILED AND EDGE-PILED STOCK
With but rare exception, all stock is flat piled. In an occasional
yard 2 by 4 dimension is edge piled with the purpose of reducing the
likelihood of bowed stock, a material objection in this item. Inas-
much as both methods afford exactly the same bearing, top and bottom,
it is doubtful if there is any advantage in edge piling. Further,
the necessity for greater precision in piling to secure proper verti-
cal circulation in the pile makes edge piling certainly less desirable
than flat piling.
NUMBER OF CROSSERS TO THE COURSE
The most effective spacing of crossers between courses of stock,
depends upon several considerations. Crossers should be frequent
enough to avoid sag; otherwise bowed lumber and other types of
deformation will result, as well as interference with horizontal air
circulation. On the other hand, as the tiers of crossers are increased
in number, air movement in the lumber pile meets more resistance.
In actual yard tests to compare the relative efficiency of 3, 4, and 5
crosser piles of 16-foot pine stock, little difference was found in the
amount of degrade and but slight variation in drying rate and final
moisture content. Less blue stain developed in the pile having three
tiers of crossers and depreciation from cupping was smallest in the
five-crosser pile. Within limits the crossers do not materially affect
horizontal circulation since this is primarily a movement from one
side of the pile to the other rather than from end to end; but, on the
other hand, in seasoning pine stock the greater the number of crossers
used the greater is the liability of crosser stain or blue stain develop-
ment on that part of the lumber in contact with the crosser. These
defects very generally result in the degrade of select and shop grades
and to a smaller extent of the better common grades, but in any case
they injure the appearance of the stock.
The use of three crossers on stock 12 to 16 feet in length and of four
or five crossers on longer stock is the most common practice, although
a great deal of lumber is piled on two crossers with 4 feet or more
overhang at the rear of the pile and very often an excessive number
of crossers are employed. Everything considered, maximum efficiency
can ordinarily be expected from the use of two tiers of crossers on
8-foot and shorter stock, of three tiers on 10 to 16 foot stock, and of
four tiers on 18-foot and longer stock. With a span of 8 feet or less,
the lumber will not sag, and on the other hand with each additional
tier of crossers in the pile circulation is further obstructed and, in
piles of pine, the liability to crosser stain is increased.
In the discussion of pile foundations, it was stated that each tier of
crossers should bear directly upon a stringer, and for that reason the
crosser practice should determine this feature of foundation con-
struction. Unfortunately in too many instances “the tail wags the
dog,” so to speak, and crosser practice is shaped to fit the foundations.
While a tier of crossers, unsupported by a stringer, keeps the boards
30 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
separated and facilitates air movement, the weight causes sag in the
pile at this point and consequently a greater proportion of bowed
stock.
STOCK CROSSERS AND SPECIAL CROSSERS.
Two general types of crossers are employed in air seasoning—
stock crossers and special crossers. Stock crossers come into use when
green stock is crossed with itself. Special crossers, as the name im-
plies, are strips or thicker pieces used repeatedly upon any grade or
size of green lumber. The size of stock crossers is, of course, auto-
matically fixed by the dimensions of the stock piled. The special
type, however, is usually 4 inches in width, although occasionally 6
inches, and 1 or 2 inches thick. The use of stock for crossers permits
rapid piling, increases the capacity of the piles, and eliminates the
necessity of carrying a large amount of stock in the form of crossers.
This practice, however, results in serious depreciation losses which are
avoided in the use of special crossers.
The stock crosser is subject to heavy degrade from season check
and is also largely responsible for this defect in the piled lumber.
Checks develop in those sections of the crosser which come between
the tiers of stock, or, stated in another way, in the parts which he
within the vertical fiues. At these points both faces are exposed to
the air, and drying proceeds much more rapidly than in the adjacent
sections which are covered, top and bottom, by the green stock. The
resultant uneven shrinkage causes checking in the portions which
dry quickly. (PI.6,B-land4.) A similar difference in drying rate
between the crossed and uncrossed portions of the lumber causes like
defect. In pine lumber conditions are highly favorable for blue-stain
development in these extremely slow-drying intersections of the stock
and crosser. The so-called “ crosser-stain” blemish is therefore a
common result of self-crossing pine lumber. (PI. 6, B-2 and 3.)
The wide green stock crosser at the front and rear of the pile also
causes excessive end checking. This results from the very marked
difference in drying rate directly at the ends of the stock and in the
adjacent sections which are between the crossers. ,
These very objectionable results of air seasoning are greatly mini-
mized through the use of the special crosser. Special crossers being
narrower and usually air-dry, or partly so, have less tendency to
check. Furthermore, stock of relatively low value can be utilized for
this purpose. Air-dry, narrow crossers, if properly projected be-
yond the ends of the stock, vary largely eliminate end checking.
Not only are the conditions less favorable for stain development but
the area affected is more restricted.
The relative merits of these two methods of crossing Western soit-
wood lumber have been thoroughly investigated by means of con-
trolled yard tests in different regions and with several species. Com-
mon pine in the Inland Empire seasoned in self-crossed piles showed
depreciation which averaged 14 per cent greater than that in com-
parable special crosser piles—4 per cent greater degrade in the piled
stock and 10 per cent in the crossers. The actual loss per 1,000 feet
of stock piled in drying No. 2 common pine was over $2 more in the
stock-crosser piles and the drying rate was slower, the lumber requir-
ing one to four weeks’ additional time to reach an average air-dry
THE ATR SEASONING OF WESTERN SOFTWOOD LUMBER 31
condition. The stock crossers showed a final moisture content about
5) per cent higher than the stock itself.
Startling as these actual degrade losses (almost entirely from
checking) in self-crossed common pine may appear, they do not tell
the whole story. The stock piled on itself showed 68 per cent of the
ends checked as against 16 per cent for that piled on special crossers.
In self-crossed piles an average of 85 per cent of the pieces showed
end checks 4 to 8 inches long, and over 50 per cent were checked at
beth ends. In addition, 22 per cent of the self-crossed stock was
stained, as compared with 10 per cent by the other method. Although
such seasoning defects do not ordinarily cause degrade in common
pine, they do mean a “harder” or lower average grade. ‘his is
certainly a consideration when the lumber is sold in competition with
similar stock seasoned on special crossers. A bright product with
little end check is surely a trade advantage.
In Douglas fir common, it was found that degrade in the stock
crossers because of season check is likely to range from 25 per cent in
1 by 8 inch stock to 75 per cent in 1 by 12 inch. In 8/4, or 2-inch
No. 1 common, such degrade was almost negligible, but in 2-inch
select common it averaged from 10 per cent in 2 by 8 inch stock te
25 per cent in 2 by 12 inch. These investigations also showed that
season-check degrade of the regular stock in self-crossed piles is
largely due to the use of stock crossers. This varies from 2 per cent
in 1 by 8 inch No. 1 and select common to 20 per cent in 1 by 12 inch.
With 2-inch No. 1 common, such degrade is negligible, but it ranges
he 2 per cent in 2 by 8 inch select common to 15 per cent 1n 2 by 12
inch.
In practice the choice between special and stock crossers varies
greatly with the region and species. In the Inland Empire all No.
3 shop-and-better pine is air seasoned on special crossers, and prob-
ably 50 per cent of the yards are piling some common in this manner.
Other species are very generally self-crossed. In the California pine
territory the practice with No. 3 shop-and-better is similar, and the
use of special crossers with the common and box grades of pine is
increasing. In the Douglas fir region, owing apparently to the
fact that selects are not air seasoned and that the species handled do
not stain, self-crossing is the common practice. Methods vary widely
between redwood plants, but although stain is not a factor special
crossers are often used.
Increased use of the special crosser is a definite need in all these
regions. ‘There is no question that its use on select and shop grades
is entirely justified, and on certain grades of common it will avoid
depreciation losses amounting to far more than the additional oper-
ating cost. The added expense, including the extra handling and
piling cost as well as the depreciation of the special crosser, is very
generally placed at 25 cents per thousand feet of stock piled. But
even if this figure is doubled, an appreciable net saving is generally
ae in addition to the production of brighter lumber in the higher
rades.
Although the extent to which special crossers can be used is largely
an individual-plant problem and one that justifies thorough study,
certain general standards can be cited. Special crossers should
ordinarily be used with pine for 8-inch and wider No. 3 common-
32 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
and-better, and with Douglas fir and western larch for 1 by 8 inches
and wider No. 1 common-and-better, and 2 by 8 inches and wider
select common-and-better; with at least the standard and better
grades of redwood 8 inches and wider; and with at least the select
grades of other species.
It is not uncommon to find special crossers used only at the rear
of the pile or at the rear and center. ‘The idea back of such methods
is that the rear and center crossers are subject to greater deprecia-
tion than the front crosser. This theory does not, however, appear
tenable upon review of the underlying causes of crosser depreciation,
nor is it substantiated by the results of actual yard comparisons.
What little variation in degrade occurs in the different tiers of
crossers runs slightly higher in the front crossers and lower in the
rear and center crossers.
DIMENSIONS OF THE CROSSER
The dimensions of the crosser have a very direct bearing upon
seasoning. The influence of the width has been brought out forcibly
in the preceding discussion. Special crossers should not exceed 6
inches in width, and 4 inches is preferable. Width of the stock
crosser is usually fixed by that of the stock piled. When random.
width lumber is self-crossed, the use of the 4 and 6 inch widths for
the crossers should be definitely insisted upon, since much deprecia-
tion can thus be avoided.
Thickness of crossers is a very important item in seasoning prac-
tice. The necessity for adequate horizontal circulation in the lumber
pile, and more particularly within the lower third to remove the
moist air which drops into this section from above, has been em-
phasized. Obviously, this horizontal air movement is assisted by
any increase in the thickness of crossers. Further, this means of
increasing circulation in the pile is a very flexible one, since the
crosser thickness can be increased in the lower section or wherever
a more positive air movement is desirable, by the simple expedient
of doubling the crossers at such points. And if an even greater
opening is desired at intervals, three or more crossers can be em-
ployed in the same manner.
Crosser thickness, where seasoned crossers are used, may be the
key to the solution of serious drying difficulties. Horizontal circula-
tion in the pile may be increased by this means wherever it is most
needed. ‘The usual lag in drying between the upper and lower parts
of the pile can thus be greatly reduced. Stain development, most
severe in the lower sections, can be greatly retarded by doubling
crossers in this part of the pile, without inviting the increased de-
preciation that would result from an equally rapid drying in the
upper sections. All of these definite advantages have been thor-
oughly tested by numerous comparisons in the different regions.
In an attempt to cut down the time required for drying redwood
the relative merits of various crosser thicknesses were studied. It
was found that stock piled on 4/4 (1-inch) crossers required 36 per
cent more time, and stock on 6/4 crossers 10 per cent more time to
become air-dry than did that on 8/4 crossers. For the California
pines, an increase in the crosser thickness not only increased the rate
Dept. Bul. 1425, U. S. Dept. of Agriculture PEATE at
A.—Kight-inch horizontal opening in lower part of pile
B.—A common method of single-length roof construction
Dept. Bul. 1425, U. S. Dept. of Agriculture
ALIN AnT
F
Y]
TA
Neen nar
|
HRI
ne
PLATE 8
oe
|
i
;
THE DOUBLE-LENGTH OVERHANG TYPE OF ROOF IS ILLUSTRATED IN A
In B and C are shown good examples of the care in actual piling that is fully as important in softwood yards as is the adoption of improved methods
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 33
of drying but materially reduced degrade from stain. Seasoning of
these woods on 8/4 crossers resulted in a depreciation of 8 per cent;
on 6/4 crossers, in a depreciation of 13 per cent; and on 4/4 crossers,
in a depreciation of 28 per cent.
The 4/4 crosser commonly used in the Inland Empire is mainly
responsible for the appreciable lag in rate of drying between the
bottom and the top of the pile. Naturally, blue-stain depreciation of
pine stock at the bottom is heavy. The effect of 8/4 crossers in the
lower third of the pile was compared at several plants and was found
to average consistently less drying time than was necessary in piles
with 4/4 crossers throughout. The stock on the 8/4 crossers reached
an air-dry condition on an average three and one-half weeks earlier
than that in the lower third of the other piles. Blue-stain develop-
ment was less than one-third of that in 4/4-crossed stock. The final
average moisture content of the stock on the 8/4 crossers was also
lower, and the customary lag in drying time between the top and
bottom sections of the piles was much smaller.
With pine, the use of two instead of one of the regular 2-inch
crossers at evenly spaced intervals in the bottom half of the pile
reduced the average degrade from 24.6 per cent to 12.9 per cent.
Similar comparisons with redwood showed a reduction in degrade
from 18 per cent to 5 per cent, and during a six-month drying period
the stock piled with double crossers lost 28 per cent more moisture.
Such methods are not only effective in building up the horizontal
circulation but are easily applied in the yard. The use of two sizes
of crossers in the individual yard is objectionable, of course, but this
is unnecessary. ‘Two or more crossers of the customary thickness
placed one on top of the other answer the purpose nicely. I, instead,
4 by 6 by 12 inch blocks are placed under single crossers at inter-
vals, this not only permits increased sidewise circulation but also
gives entrance to the wind currents in the front and rear alleys, which
are normally shut out by the crossers. (PI. 7, A.)
The actual practice in the West varies greatly. In the Douglas fir
region, where practically all stock is self-crossed for air seasoning,
the thickness of the crosser conforms to that of the lumber being
piled. The 4/4 crosser is the general standard in the Inland Empire,
although some pine shop and selects, especially 5/4 and thicker stock,
are piled on 8/4 crossers, and the practice of opening up the lower
part of the pile with thicker crossers is increasing. In the California
pine territory the 8/4 sticker is the standard. Strangely, in the
redwood region, where slow drying is the big problem, the 4/4 sticker
is commonly employed.
In any attempt to improve seasoning conditions the question of
crosser thickness must be analyzed carefully. It should be clearly
recognized that positive horizontal circulation, particularly in the
lower part of the pile is a very necessary adjunct to the natural
downward air movement in the lumber pile. Horizontal circulation
is imperative ii the lag in drying between the upper and lower
halves, and hence the average drying time, is to be satisfactorily
reduced and depreciation, chiefly from stain, is to be avoided. Varia-
tion of the crosser thickness is the most flexible means of influencing
horizontal circulation,
34 DEPARTMENT BULLETIN 1425, U. S. DEPT, OF AGRICULTURE
SPECIES EMPLOYED AS SPECIAL CROSSERS
Various species are used as special crossers. In the Inland Em-
pire the larch-fir strip is generally employed, although cedar and
white fir are used to some extent. The white-fir crosser is most com-
mon in the California pine region, Douglas fir being second in im-
portance for this purpose. Douglas fir is also the chief species used
in the redwood territory. In the Douglas fir region the practice of
self-crossing stock fixes the kind of crosser used. |
At any plant, availability of suitable species and grades plays
an important part in the kind of crossers used. But within such
limitations, three considerations should serve as guides. Where pine
is to be seasoned, susceptibility to stain is of first importance; ob-
viously, species and grades which do not favor stain development
should be selected. Mechanical properties which will enable the
crosser to stand up under the usual wear and tear incident to such
use are also necessary. And the value of the material utilized of
course bears directly upon the investment which must be carried,
as well as upon the amount of the actual losses due to breakage and
other forms of depreciation.
CONDITION OF THE CROSSER
It is customary at a majority of plants to use special crossers_
repeatedly until they are worn out. Some of the more progressive
companies, however, attempt systematically to dispose of this crosser
stock after it has been used three or four times. This is a very
desirable practice, especially in yards where pine is handled. Not
only does this permit the sale of such stock before it is seriously
depreciated (probably a drop of one grade on the average), but
it also avoids the possibility that with prolonged use the crossers may
become a source of blue-stain infection. Although the crossers may
be made of species not susceptible to blue-stain development, their
use on stain-infected pine stock and careless handling and storing
about the yard soon results in their collecting blue-stain spores which
readily transmit new stain infections to the piles of freshly cut pine.
Actual comparisons to determine the effect of the age of the crosser
upon crosser-stain development showed that stock piled upon old
crossers was stained two-and-a-half times as much as that piled on
new seasoned crossers. This same test brought out the fact that the
use of green crossers resulted in four times as much crosser stain as
did the use of new dry crossers. Investigation also indicates that
a rough crosser causes less stain than a surfaced crosser. Unques-
tionabiy, rough seasoned crossers which are disposed of after a short
period of use will give the most satisfactory seasoning results.
PLACEMENT OF THE CROSSER
After the general plans for crossing stock has been settled, stand-
ard methods for the actual placement of the crossers should be
adopted. Periodic yard checks are then necessary to see that the
prescribed standards are being carried out in practice. The place-
ment of crossers, as practiced throughout the West, embraces both
good and bad practice. One of the most general violations of good
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 39
practice is that of improper bearing of the crossers. Bowed stock
and other forms of depreciation result from crossers not bearing
directly on those beneath. The vertical alignment of each tier of
crossers should approximate the pitch of the pile. The front crosser,
and the rear crosser in box piles, should be consistently placed so
that they project beyond the ends of the stock. When stock 6 inches
and wider is self-crossed, at least 2 inches of the crosser width should
overhang to avoid end checking, and where 4-inch special crossers
are employed this overhang should be at least 1 inch. The difficulties
of this method are greatly exaggerated and the merits fully justify
insistence upon its use. Observation alone should convince any one
of the effectiveness of this practice, even if actual pile comparisons
did not fully substantiate it. In pine stock piled with the crossers
flush with the ends, eight times as much check developed as in stock
protected by overhung crossers. A similar test with inch Douglas
fir stock showed end checking of 20 and 3 per cent, respectively, when
the two methods were employed.
Some yards using stock crossers, particularly stock 8 inches and
wider, stagger the center and rear crossers about half their width.
(Pl. 5, D.) By this method, the portion of the board ordinarily
covered on both sides by the crosser is exposed to the air on one side.
This results is a shghtly lower final moisture content in these sec-
tions, and it is said that less checking of stock and crossers occurs.
On the other hand, such practice does not lessen crosser stain and,
especially with 4/4 stock, invites depreciation in the form of bowed,
warped, and twisted lumber.
SPACING BETWEEN BOARDS
A. fundamental principle of air-seasoning and one which appar- |
ently fails to receive proper recognition in yard practice, is that
there must be vertical air circulation in the lumber pile. This in-
ternal downward movement resulting from the natural tendency of
the moist air, cooled by evaporation, to drop toward the bottom
of the pile, must be positive throughout the pile in order to make
the drying process most effective. Best results are therefore obtained
when lumber is piled in even widths, permitting unbroken vertical
flues extending from the top to the bottom of the pile between each
two tiers of boards. In random-width stock such construction is
ordinarily impracticable, and, accordingly, a relatively wider spacing
between boards in the course is necessary to offset as far as possible
this disadvantage.
The interval between boards can to some extent control the rate of
drying. Extremely rapid drying and consequent depreciation from
checking can be moderated by a reduction of this spacing. On the
other hand, the drying rate can be increased, the lag in drying
between lower and upper sections of the pile can be decreased, and
blue-stain losses reduced by a greater spacing. One obstacle, how-
ever, to control of drying rate by spacing is that wide spacing reacts
proportionately in all parts of the pile and thus may improve the
drying process in one portion at the expense of creating a more
serious condition in another. Hence, spacing must be supplemented
by other methods in order to obtain the most uniform drying.
36 DEPARTMENT BULLETIN 1425, U. S. DEPT, OF AGRICULTURE
To determine the relative efficiency of different spacings with
even-width stock, tests were conducted on both select and common
grades of pine during different seasons of the year and at several
plants in the inland empire. The results obtained (Table 5) were
very consistent and point conclusively to a definite relationship
between drying conditions and width of spacing. They show that
the rate of drying is materially affected. Stain losses can be greatly
reduced by increasing the spacing, and increases of the interval up
to 4 inches at least do not appreciably increase the occurrence of
DESCRIUIGN, Of5 FYLE SS
STOOGKAS AE AVE NE COPUUN HESTERN HEUTE PIME
BOK TIPE PILES
V6 FEET SQOUARL VIO COURELS
VX CROSGSLRE :
CAT. SLANG BETHEL BOACDE-2,3 AND 2°
8
40
Moisture content, per cent
20
10
°
LF LOM 27 (ES 10 IF 24)\t 8 eG Ae FES LAS TON FS NE 100 (U7 Zea Ne
DEC. JAN.
AUG. SEPT. OCT. NOV.
Fic. 5.—Comparative ‘ pile average”’’ drying rates for stock piled with different
spacing between boards
shrinkage defects. Figures 5 and 6 allow a visualization of the
influence which the spacing exerts upon drying rates. Figure 6 also
indicates that by this means the lag in drying in the lower part of
the pile can be to some extent reduced.
TABLE 5.—Effect of different spacing between boards in the lumber pile
f Degrade Loss per M feet Final | Time re-
Gia cinigy i See COS: fist Lhe evn doves lL poh edi Ulaleenks eal is see eR OTS hl AGERE
stained ture for air-
Stain | Check | Knots} Total | Stain Check | Total |content} drying
Inches |Percent| Per cent| Per cent| Per cent| Per cent Percent| Weeks
4 FL Sard 0. 4 1.8 5.9 $0. 57 $0.07 | 1$1. 25 15. 5 15
3 29. 4 6. 4 2 255 9. 2 1. 33 .16 12 BB" 15.0 18
2 38. 4 10.5 5 UI 2. 4 13. 6 1. 75 14 1 2. 87 15.7 25
1 Total figures are not the sum of those in the 2 preceding columns.
‘The practice of spacing even-width western softwood lumber for
air seasoning is naturally far from uniform. The numerous species,
grades, and sizes involved, the great variation in general piling prac-
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 37
tice, and differences in natural conditions present a variety of prob-
lems. However, the wide differences in practice indicated below are
too largely the result of failure to appreciate fully the basic relation-
ship between spacing and the drying process and so to give recogni-
tion to it in pile construction:
Region Average
spacing Range
E Tees Inches Inches
SE AnTORMAAyDING Ake.) eset ee kee asks). bs | i ADO LE IE Re OREN aos 4 4 2-8
ine binipirotas. 352 SV 5 i NPE) te yey eee FY 3 1-6
Re WOCd meee ee ERNE Tk oy OE eS Soe SE eC 12 Y-2
1D Yayo ed NS Fi Vins Se en ah ae he Be ee A DE To SR A Ae De Se hee 121% V4
1 Approximate.
Proper spacings must be worked out at each plant, due weight
being given to the facts presented here. Coordination with other
requirements in pile constructions is also essential. As a general
guide, it may be stated that wide stock requires a greater spacing
80
DESCRIPTION OF PILES
STOOKSNE ME Wh? tlt PESTLE HITE PUNE
BOX TVPE PILES
V6 FEET SQACE SIO COURGELS
VXE CROSGSELRE
SLANG BETHELW BOARDS 22 AND F
Moisture content, per cent
°
12 20 27), 3 10 17 24.)\( 7 8 15 22 29) S 12 19 26)\ 3 10 17 24 63 ee
OCT. NOV. DEC.
AUG. SEPT. SAN
Fic. 6.—Comparative drying rates in lower third of pile for stock piled with different
spacing between boards
than narrower stock, 5/4 and thicker stock requires more than 4/4
stock, and pine, because of its susceptibility to stain, more than other
species. A dual system may be necessary to meet the drying ex-
tremes of different seasons. Standard practice may call for a
narrower spacing during the active drying season than will meet the
needs during the rest of the year.
In piling random-width stock, the usual practice of allowing a
fixed interval between boards irrespective of their width permits no
unbroken flues from the top to the bottom of the pile. As stated be-
38 DEPARTMENT BULLETIN 1425, U. S. DEPT, OF AGRICULTURE
fore, a relatively wider spacing is necessary than for even-width
stock in order to offset this lack of well-defined channels for vertical
circulation. The effect of increased width is well shown by actual
yard comparisons. Random-width 6/4 No. 1 shop-and-better sugar
pine piled with a 38-inch spacing resulted in a total degrade of 11.8
per cent; with a 5-inch spacing, in a degrade of 5.3 per cent; and
with a 7-inch spacing, in a degrade of 4.8 per cent. The reduction in
stain development accounts for practically the total difference be-
tween the first and second tests. Although stain was practically
eliminated by the 7-inch spacing, increased defects resulting from
very rapid drying largely discounted that advantage. ‘This indicates
that methods of hastening seasoning must not be carried too far.
Although in each region the spacing allowed in piling random-
width stock averages slightly larger than that employed for even
widths, a still wider interval is very generally needed. At numerous
plants a real improvement in seasoning conditions can be obtained
by this means.
CHIMNEYS OR VENTS
Very closely related to proper spacing is the procedure of building
chimneys or vents into the lumber pile as a means of improving
vertical circulation. Chimneys are unobstructed vertical openings
quite distinct from the flues obtained by the uniform spacing of even-
width stock. They are normally wider than flues and are located
only at the center of the pile or at definite intervals across the width
Their most effective use is with random-width stock.
Little uniformity in the practice of using chimneys is evident, and
this results in large measure from a lack of accurate knowledge of
the real influence of this feature of pile construction upon actual
drying conditions within the lumber pile. At some redwood plants
both even and random width stock are piled with two chimneys 10
to 16 inches wide, and at others no chimneys are employed. In the
California pine territory the chimney is little used with even widths,
but the straight center vent 8 to 20 inches wide is very generally
utilized with random stock. Inland Empire plants rather commonly
pile even-width pine with an 8-inch center chimney and employ a
large assortment of vent combinations in the seasoning of mixed
widths. A 6 to 12 inch center chimney is most common. Two 8 or
10 inch chimneys are not unusual, and some plants make use of from
three to eight narrow vents distributed across the pile. Chimneys
find little use in the Douglas fir region and where employed are
generally of the single center type.
Since the only purpose of chimneys is to aid vertical circulation
throughout the lumber pile, it is more logical in seasoning even-
width stock to increase the spacing between the boards in a course
and thus the width of the vertical flues, than to use a relatively nar-
rower spacing and place a center chimney in the pile. This con-
clusion has been confirmed by numerous actual yard comparisons of
the results obtained from both methods of piling. At several plants
in the Inland Empire even-width pine stock piled with a 3-inch
spacing was air-dried in less time and developed slightly less stain
than did the same stock piled closer and given a 12-inch center
chimney. In the Douglas fir region, piles with 2-inch spacing and a
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 39
10-inch vent at the center failed to show any increase in either the
rate or uniformity of drying over piles with a 3-inch spacing and
no vent.
An adaptation of the chimney method may, however, be used to
advantage with even-width stock in yards where the evils resulting
from slow drying in the lower part of the piles are a primary prob-
lem. What are in effect short chimneys are formed by simply elimi-
nating every other board in the course for the first 4 or 5 feet of the
pile. The merits of such a method are the increase of vertical circula-
tion in that part of the pile where it is most needed at a sacrifice of
space in that section alone. The obvious disadvantage, that of insuf-
ae bearing surface for the crossers, is not serious except with wide
stock.
The use of chimneys in piles of random-width stock is of course
entirely justified. It is, indeed, the only practicable means of creat-
ing a direct vertical circulation in piles of this type. The single
straight center chimney is undoubtedly of value, but the rate and
degree of drying attained are far from being as favorable as those
obtained in properly constructed even-width piles; and stain losses
are usually very heavy. Two chimneys are likely to give better
average conditions, although the center section of stock between them
is probably subject to more severe stain depreciation. The center
A-shaped or “ flared ” chimney, 8 inches in width at the top and 22
inches wide at the bottom, is superior to either single or double
straight chimneys. It not only makes a maximum provision for
vertical circulation where that is most needed but in so doing elimi-
nates stock from that part of the pile which is subjected to the very
worst drying conditions. This method is also economical of space
in the upper sections.
If three to eight chimneys are employed, evenly distributed from
one side of the pile to the other, an approach is made to the desirable
conditions obtained in piling even-width stock. Positive vertical
circulation throughout the pile is more nearly attained. Within each
of the four to nine vertical sections of stock thus set apart the
boards in a course should be placed as nearly tight as the widths
will permit when the outer boards of each section are kept flush
with the sides of the chimneys. This general system has advantages
over the other chimney methods discussed. The pile capacity is
greater because of the relatively narrow chimneys, usually 6 or 7
inches, and the close piling between them. The rate of drying is
more rapid, and less stain develops as a consequence. Degrade from
checking is also smaller because, although the chimneys allow good
vertical circulation, the principal effect of this is to build up the
horizontal air currents that permit uniform drying across the face
of the stock. On the contrary, with fixed spacing between the boards
in a course, short flues occur blocked above and below by wider
boards. Air currents following these flues strike the projecting
board and effect an unequal drying that often causes checking.
Controlled yard tests of these several methods show clearly that
the use of chimneys in random-width stock has a very definite effect
upon drying and indicate the relative merits of the different methods.
Comparisons were made of the pile without chimneys, the pile with
two 12-inch chimneys 414 feet apart, and the pile with a center flared
AQ DEPARTMENT BULLETIN 1425, U. 8S. DEPT, OF AGRICULTURE
chimney 8 inches wide at the top and 22 inches wide at the bottom.
Random-width 6/4 shop and select western yellow pine stock was
used in all piles. Pile construction without chimneys resulted in a
total degrade of 24.6 per cent, as compared with 16.6 per cent from
the two-chimney method and 9.2 per cent from the use of the flared
chimney. Most of the depreciation in all piles resulted from stain,
the rate of drying being fastest in the flared-chimney pile and slowest
in the no-chimney pile.
The results obtainable from the common 12-inch center chimney
were compared with those from piling with five 7-inch chimneys
evenly distributed across the pile and the boards on a course placed
approximately solid within the six vertical sections of stock.
Random-width 4/4 select western white pine stock was used. The
five-chimney method resulted in 10 per cent less stain development,
a 3 per cent smaller degrade from stain, and only halt the loss from
season check. The actual degrade loss was $2.75 per thousand less
by the five-chimney method, stock reached the air-dry condition two
weeks earlier, and the final moisture content was shghtly lower.
As is true with all phases of pile construction, the use of chimneys
or vents must be adapted to the situation at each plant. It is pos-
sible, however, to set up some very definite principles as a guide. In
piles of even-width stock the use of chimneys is not as effective as
is an equivalent increase in the width of the unbroken vertical fiues
between the uniformly spaced boards. In piling random-width stock,
a single straight center chimney at least 12 inches in width is an
improvement over no chimney; but less piling space is sacrificed and
much more efficient seasoning is obtained by the use of three or more
smaller chimneys evenly distributed across the width of the pile.
Where three or more uniform chimneys are impracticable, as is often
the case with very wide shop and select grades of California pine,
a single flared chimney at least 22 inches wide at the bottom will
prove more effective than a single straight chimney.
It should be realized that the use of chimneys is only one of sev-
eral means to obtain more efficient drying within the lumber pile.
If sluggish drying is to be overcome, any system of chimneys must
be supplemented by one or more of the other means.
ROOFS
A good pile covering improves seasoning by protecting the stock
from rain and snow and from full exposure to the direct rays of the
sun. Some operators believe that, at least during seasons of light
precipitation, lumber seasons more rapidly in unroofed piles. What-
ever slight advantage there may be in this practice is, however, more
than offset by its disadvantages. In seasons of sparse rainfall, when
the most rapid drying can be expected in unroofed piles, the direct
exposure to the sun and the consequent excessive rate of drying
cause heavy depreciation from cup, warp, twist, and check in the
upper portion of the pile. At no time is alternate drying and wet-
ting of stock an aid to seasoning; generally it only invites
depreciation.
Stock is commonly roofed with itself or with special roof boards.
Special roofing has definite advantages. It is possible to utilize
material of the size best adapted to the purpose and of the species
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 4]
and grades of lowest value. Use of cheaper lumber is very important
because of the high depreciation of roof boards. In actual checks of
such depreciation, when No. 2 common-and-better pine stock was
self-roofed, 70 per cent dropped at least one grade. If No. 3 or No. 4
common were used to roof the better stock, a net saving of $2 could be
made on each pile, over and above depreciation and extra handling of
the special roof material. Although practice must, of course, be in
accord with the local situation, since the price differential between
grades varies with the species and climatic conditions also have a
direct bearing upon the depreciation of roof boards, yet, as a general
rule, the select and shop grades of all species, No. 1 and No. 2 common
erades of pine, and if possible the upper common grades of other
species, should be covered with special roof boards. This now con-
stitutes the accepted practice in the majority of western yards.
The essentials of proper roof construction are, (1) sufficient pitch
to assure run-off, (2) suitable material and lapping to avoid leakage,
(8) overhang at the front and rear of the pile, and (4) some clear-
ance between the stock and the roof. Two general types of roof are
commonly employed—that which provides a front and rear overhang
and that which does not. The “overhang” type is constructed in
two ways; with boards 2 to 4 feet longer than the piled stock or with
double lengths of boards. The former method requires the use of
special rood boards while the latter may be built with stock. The
second type of roof, that which does not project beyond the ends of
the pile, is constructed cf boards the same length as the stock and is
most commonly used when stock is roofed with itself.
Plate 7, B shows the common method of single-length stock roof
construction. It consists of two layers of boards, the top course lap-
ping the lower course of boards which are spaced several inches apart
upon supporting stringers. These stringers, which bear upon the
crossers and usually consist of crossers or stock laid one upon the
others, form supports of different heights, the center lower than the
front and the rear lower than the center. The double-length roof,
as illustrated by Plate 8, A, is simply an adaptation of the former
to give overhang at the front and rear of the pile.
Adequate overhang of the roof at the front and particularly at the
rear of the pile is very desirable. This gives some protection from
rain and snow beating in at the ends of the pile, and by the shade
afforded tends to avoid end checking in the stock on the upper
courses. It also allows the drip from the roof to fall clear of the pile.
The need for sufficient pitch to secure good run-off is obvious. The
clearance between the roof and the stock is ordinarily sufficient for
air circulation if adequate pitch is provided. Little difference in
effect upon seasoning was indicated for roofs 1 inch, 6 inches, or 10
inches high, although the rate of drying in the upper third of the
pile may be slightly increased with the higher roof. The use of
several crossers to hold the roof boards in place is usually satisfactory,
but in windy situations or period of the year it is generally advisable
to fasten rocfs to the piles with wire or roof irons.
Although the tendency toward improvement in the style and work-
manship of roof construction is very noticeable in the West, much
can yet be done along this line. All stock should be roofed during
air seasoning. Ordinarily, the use of stock roofs is justified only on
the lower grades of common lumber. Adequate overhang, at least
42 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
12 inches at the front and 214 feet at the rear, is essential. A pitch
of 1 inch to each foot of length is required to assure good run-off, and
the height of the roof over the rear tier of crossers should best be
about 4 inches. Drip boards, sometimes used with roofs that have no
overhang to throw drip away from the rear of the pile, are praised
by some and condemned by others. However, this method is far less
effective than the overhang type of roof.
SUMMARY OF METHODS FOR IMPROVING DRYING PRACTICE
It has been stated, and the preceding discussion of the entire air-
seasoning process must certainly have led to the very definite con-
clusion, that the air- -seasoning problem can not be solved by “ cut-
and-dried ” rules. Neither the present discussion, based though it is
on comprehensive and detailed studies, nor any ‘other intensive in-
vestigation of air seasoning, can alone determine efficient practice
for every yard. Fundamental information on drying can be given
and its application indicated in a general way. This material may
be used by the individual as a guide, but only as a guide, in work-
ing out his own problem. He “must give much time and effort to
checking for his own yard the effect of different methods and com-
binations of methods upon stock depreciation, rate of drying, final
moisture content, operating costs, and yard-space requirements. And
such time and effort can without question be made productive of
handsome financial return through greater efficiency in air seasoning.
Will these very definite though intangible returns be appreciated at
their full value and prove an incentive to improved yard operation ?
The small plant, whose yard crew may consist of two or three men
working under the direction of the man in charge of the entire manu-
facturing operation and the great plant having an enormous daily
production, with its yard superintendent and assistant, green and dry
lumber foremen, stock clerks, piling crews, dry- lumber handlers,
transportation crews, trackmen, foundation- repair men, crosser men,
and clean-up men, both have one thing in common. The men who are
qualified and who naturally should have the incentive to check and
study seasoning methods in relation to actual results are so pressed
with supervisory and other duties that little thorough work of this
nature is possible. To this situation the majority of the difficulties
and failures in air seasoning can very largely be charged. Real effi-
clency in air-seasoning practice must have accurate detail knowledge
for its basis.
Indirectly, the major objectives of air seasoning are obtained by
control of the drying rate. The aim of any method is therefore pri-
marily to create conditions conducive to either faster or slower drying.
The more general principles of bringing such conditions about should
accordingly be summarized.
If more rapid drying generally is desired, the means most ap-
plicable are the following:
Improved yard drainage.
Hradication of vegetation.
Wider spacing between sides of the piles.
Higher foundations.
Narrower piles.
Thicker crossers.
Wider spacing between boards.
Chimneys in random-width stock.
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 43
To obtain faster drying in the lower part of the pile and thus
decrease the differential in rate of seasoning between the bottom and
top sections and to reduce as well stain development in the lower
portion without increasing the rate in the upper part, the following
methods are of value:
Thicker crossers in lower third of pile,
Horizontal openings at intervals.
Short chimneys at bottom of piles of even-width stock.
Flared chimneys in random-width stock.
The elimination of stock depreciation resulting from excessively
rapid drying, which usually occurs in the upper half of the pile, can
be attained with little slackening of drying in the lower half by such
practices as—
Narrower spacing between piles.
Thinner crossers in upper half of pile.
Narrower spacing between boards,
In the development of air-seasoning practice the manner in which
piling is done is a consideration of major importance. No matter
how efficient are the methods adopted, the results are in no small
measure dependent upon the actual construction of the individual
pile. Flues and chimneys must be carried up without being ob-
structed by carelessly misplaced boards. (Pl. 8, B.) In random-
width stock if less than three chimneys are used consistent spacing
between boards is essential. Each crosser should bear directly on the
one beneath. (PI. 8,C.) The front and rear crossers should always
project beyond the stock to afford protection to the ends. (PI. 8, B.)
When random-width lumber is crossed with itself, reasonable effort
should be made to select the narrowest widths for crossers. Finally,
careless handling should not be tolerated, since this can mean a very
appreciable loss.
Any means of supervision or system of payment for piling that
will assure careful pile construction should be followed. Observa-
tion in numerous yards indicates that piling by men paid day wages
usually comes nearer to consistent attainment than does the contract
method. An increase in the piling cost of as much as 25 cents per
thousand feet looks small in comparison with some of the proved
savings from reduced depreciation. One principle should be firmly
fixed: Improvement of the air-seasoning practice is of first impor-
tance, and prejudices and preferences of the lumber piler as to the
manner of doing his work are secondary.
REGIONAL AIR-SEASONING PROBLEMS AND THEIR
SOLUTION
INLAND EMPIRE PINE REGION
GENERAL CONDITIONS
The pine-producing region known as the Inland Empire is usually
considered as embracing Montana, Idaho, and those sections of Wash-
ington and Oregon east of the Cascade Range. Naturally, within a
territory of this size considerable variation in weather conditions is
found. The region, as a whole, is, however, distinguished by certain
common climatic characteristics which exert rather definite influences
44 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
upon the air seasoning of lumber. Figure 7, although based on
weather data obtained only in western Montana, northern Idaho, and
eastern Washington, illustrates characteristic features of the Inland
Empire. Two well-defined periods are indicated—an active drying
season which ordinarily extends from April 15 to October 10, and a
much less favorable period of drying during the remainder of the
year. Particularly in the spring and fall, warm days with relatively
high humidities are common. Such conditions are ideal for blue-
stain development. During the summer months periods of extremely
low humidity cause excessively rapid drying.
The kinds of lumber produced, of course, influence the seasoning
practice. Western yellow pine, now designated pondosa pine by
| Aur racroR yan yes yrarlaceyia ine Wel S22) 067 WO 0E|
|
COMPARATIVE MONTHLY WEATHER CONDITIONS
PER CENT | TO
PELATIVE
AHlUMIDOI TY
OP
TE/IPERATURE
oc
T | I I |
ACTIVE DRYING SEASON
7 SS
Pe wy
~
=
x
RELATIVE HU/MIDITY-PIONTHLY AVERAGEEPNIS.
0° <== TEMPERATURE - MONTHLY AVERAGE 4PM. N.
AVERACE LRIIWG FLERIODS Fie ST0LK PULLD MM LUEFERLAT (UWTBE 70 REACH IE PE CENT WIEST COWIEWT
acoseenncrvere yz0\a0 [eo oo] 20 | ze| 20) 20 | 20
ADR OUNMATE JAOVSTLIPE CONTENT OF THOROL CGAL APLC STOCK LY MONTHS
PER CENT
I \WCOlSTWE CONTENT | Zor| ZO#\/B+\ 7S | (4 \ (2 \/ZA\ IB \ 4 | LS#\ZO4\LOF
MVERAGLE PICKLP OF UZUISTURL BR YARD SIOCK AT LDI-FERENT SEASONS
TIE
Fic. 7.—Graphic air-seasoning chart for the Inland Empire
the industry of the Inland Empire, constitutes nearly half of the
annual cut. The western white pine, or Idaho white pine, is next
in importance, although the combined production of larch-fir exceeds
that of the white pine. White fir is also cut in appreciable volume.
Western red cedar, Engelmann spruce, western hemlock, and lodge-
pole pine are of comparatively minor commercial importance.
(Table 1.) |
Certain manufacturing practices characteristic of this territory
have a real bearing on the air-seasoning problem. The region is
primarily a “board” producer, a very large proportion of the cut
being in the form of 4/4, or 1-inch stock. Only a small quantity
of pine is cut heavier than 6/4. Larch-fir goes into 2-inch and
thicker products to a greater extent than any of the other
regional species. Considerable 6/4 white fir is now cut. Most of
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 45
the board production is in widths of 12 inches and less, owing to
the relatively small size of the region’s timber; although wider stock
is ordinarily found in the thick sizes of pine. The average length
of the stock is about 16 feet, with the possible exception of shop and
thick select lumber.
Each producing region has seasoning methods peculiar to that
locality, for many of which it is difficult to find logical explanation.
In the Inland Empire width of main alleys is exceptionally good,
but the width of the rear alleys and the spacing between the sides
of the piles are generally inadequate. Comparatively low founda-
tions are the rule. With the exception of shop and thick select
lumber, stock is usually piled for air seasoning in separate widths
and to a much smaller extent in separate lengths. The square or
box type of pile is most frequently used and the heights are usually
90 to 100 courses of inch lumber. The 4/4 crosser is standard for
the region and the common grades are largely self-crossed. The
usual spacing allowed between boards in a course is 8 inches for
pine and 1 to 2 inches for other woods. An 8-inch center chimney
is very often built into piles of separate-width stock, the 8 to 12
inch center chimney being commonly employed with random widths.
Special roof material finds rather general use on No. 2 common-and-
better pine and on the selects of other species. The overhang type
of covering is now used at a majority of the plants.
RESULTS FROM PRESENT PRACTICE
Exact piece-depreciation records obtained for about a million
feet of stock in the Inland Empire are summarized in Table 6.
These indicate something of the losses being sustained in average
current practice. Although confined to the pines, such information
if properly analyzed permits some very definite conclusions as to
the really vital problems of air seasoning in the Inland Empire.
Certainly these results are ample justification for active interest
and attempted improvement in the air-seasoning practice.
From the standpoint of stock depreciation blue-stain prevention
is of major importance. It is the cause of serious losses in western
yellow pine and is of material consequence, though less severe in
white pine. Depreciation of this kind is naturally more severe in
the shop and select grades than in the common. With present
practice the losses are much greater in the lower third of the pile,
probably averaging two and a half times those in the upper third.
Stock piled in the spring and fall is most subject to blue stain;
winter-piled lumber is least affected. Stain is not a factor with the
regional woods other than pine.
Season-check losses and end checking are also matters of concern.
The more frequent occurrence of these defects in the common grades
results directly from the rather common practice of self-crossing
such grades, whereas shop and selects are always seasoned on special
crossers 4 inches in width. It is clearly shown that the white pine
is more susceptible to this type of depreciation than the western
yellow pine. Larch-fir and white fir also suffer losses of this kind.
Checking occurs to a much greater extent in the upper half of the
pile and, as would be expected, is of greatest severity during the
summer period.
46 DEPARTMENT BULLETIN 1425, U. S. DEPT, OF AGRICULTURE
Depreciation from knot defects is uniformly a factor with all
grades and species because of the fact that certain knots will loosen
in seasoning no matter what the system or methods employed.
Degrade of this kind is usually somewhat smaller during the inac-
tive seasoning period, owing to the relatively higher moisture con-
tent of air-dry stock at that time. Warp-bow-twist, although the
cause of material losses at individual plants, is of relatively minor
consequence for the region as a whole.
A comprehension of usual drying rates and average final moisture
contents, which apply to air-seasoned stock during the different
months of the year in the Inland Empire, can be obtained from
Figure 7. Admittedly these will differ somewhat in different yards
and in the same yard during years in which the seasons vary con-
siderably from the normal. Nevertheless, these are indicative of
the average results obtainable in air seasoning 4/4 pine stock in
this region and point to some very definite problems.
With present yard practice, stock will reach a moisture content of
15 per cent in 90 days or less only if piled during May, June, July,
and August. If piled during the period from September to Jan-
uary, more than six months is required to reach the same level.
It is also shown that during only half the year, April to Septem-
ber, it is possible to obtain a moisture content as low as 15 per
cent. Furthermore, stock which may have reached a moisture con-
tent lower than 15 per cent by the middle of September will begin
to pick up moisture at a comparatively rapid rate if left on crossers
in the yard, and by February may contain 23 per cent or more mois-
ture. Such conditions necessarily mean a relatively heavy carrying
charge for the stock and high shipping weights and unsatisfactory
moisture contents during certain periods of the year.
47
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER
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48 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
RECOMMENDATIONS FOR IMPROVEMENT
The major air-seasoning problems of the Inland Empire should be
evident. Briefly, these are (1) the reduction of blue-stain develop-
ment on pine stock, (2) the minimization of checking, (3) shorter
seasoning periods, and (4) lower final moisture contents. Without
attempting to prescribe any “cure-all” for these difficulties, nor to
outline an “ideal” practice for the specific yard, certain general
suggestions for improvement can be made, which, if followed, will
aid in the solution of the big regional problems and should assist the
local yardman in the determination of efficient practice at his own
olant. dats
Any adequate measures for the reduction of blue-stain development
will also tend to shorten the seasoning period and lower the final
average moisture content. On the other hand, most remedies for
checking are in direct opposition to such measures. But this situation
is not as hopeless as it might at first appear. Methods of blue-stain
prevention and of season-check reduction can fortunately be nicely
harmonized because of the nature of these defects. Stain development
is most severe on western yellow pine during spring and fall, in the
lower part of the pile, and on the shop and select grades and the
narrow sizes. On the other hand, maximum checking occurs with
the white pine during the summer period, in the upper part of the
pul, and on the common grades and wide sizes. It is also true that
the greatest single factor contributing to long drying periods and
unsatisfactory final moisture content is the lag in drying at the
bottom of the pile. Reduction of this lag is possible without increas-
ing the liability of checking in the upper section of the lumber pile.
General conditions surrounding air seasoning in the Inland
Empire can be bettered to great advantage, as follows:
In many yards, improved drainage, better sanitation, and current
eradication of vegetation are essential.
Wider rear alleys and an increase in the spacing between sides of
the piles are necessary.
An outstanding need is that of higher foundations.
Stock should always be piled one layer to the course.
The use of special crossers 4 inches in width is essential on 8 inch
and wider No. 3 common-and-better pine and No. 2 common and
better grades of the other woods.
The lower third or half of the lumber pile should be of more
open construction to facilitate both the vertical and horizontal cir-
culation. The 8/4 crosser should be used generally for that purpose
and in 5/4 and thicker western yellow pine throughout the pile.
In piles of separate-width stock a minimum spacing of 4 inches
between boards in a course should be allowed during the inactive
drying season, this being reduced during the rest of the year if
checking is serious. 3
Random-width stock should be given a uniformly wider spacing
unless the more desirable practice of three or more chimneys is
feasible. Finally, the practice of taking down and close piling
stock that is thoroughly air-dry at the end of the active drying
season should be greatly extended in the interest of lower shipping
weights and satisfactory moisture content.
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 49
; CALIFORNIA PINE REGION
GENERAL CONDITIONS
The California pine region includes the Klamath Falls district
of south-central Oregon as well as the pine territory of California.
It extends, therefore, from southern Oregon through the entire
length of the Sierra Nevada Range in California and embraces both
sides of that range and of the Coast Range northward from San
Francisco. However, in spite of the diversity of weather conditions
which such an extent of territory involves, the region as a whole is
characterized by certain common climatic features which to a con-
siderable degree unify its air-seasoning problems. The comparative
monthly weather data presented in Figure 8 are a composite of the
COYLARATIVE AIONTHLY WEATH LE? CONLYTIONS
] ] if T | |
Hee ACTIVE DRYING SEASO/VV
FER CENT
ALLATIVE
SVL /L/ 7
ZO
GO
OR
TEMPERATURE
or 150
MWERACE DRYING FERIOLS FOC G2 STOCK PULLD 1h LUFLERLWT MONTHS 70 REA [6 FE CELT HUSTLE COTE
APPR QMATE MOUSTUKE CONTENT OF THOMA MV ARDY STOCK By MONTITS
PER CENT
MUSTURE CONTENT \ ZO \78.\/6\/4\/2Z\/70\F | JO \/2\/76 \ 78
AVERAGE MIGKLIP OFRAUSTURE By VOD STOCK 1M OUPVERE/V 7 SEASONS
eee Wie ole be | aye [pele
Fig. 8.—Graphic air-seasoning chart for the California pine region
o x
oe x
oO ——— RELATIVE HUMIDITYS AMONTHLY MEAN
=~ TEMPERATURE ----- ~~ MONTHLY MEAN
relative humidities and temperatures encountered at several fairly
representative points and are given simply that the reader may
visualize the most striking regional features. In this area, as in
the Inland Empire, distinct active and inactive drying seasons
occur. However, the active period is of longer duration in the Cali-
fornia pine region, and the extremes are less severe, particularly dur-
ing the inactive season. This means relatively less difficulty with
rate of drying and final moisture content, but makes for a longer
seasonal period of stain danger. Conditions favorable to excessive
drying are, also, present for a time each year.
The lumber cut of this region is very largely pine. More than
60 per cent of the annual production is composed of the western yel-
50 DEPARTMENT BULLETIN 1425, U.S. DEPT. OF AGRICULTURE
low pine of which the adopted trade name in this territory is
California white pine. Sugar pine accounts for an additional 15 per
cent and white fir and Douglas fir make up the bulk of the remaining
eut. (Table 1.) a AL ptilk es
Air-seasoning practice in the California pine region is directly
affected by certain manufacturing methods peculiar to this territory.
A large proportion of selects, shop, and box lumber is cut, owing to
the size of the timber and to trade demands. This results in a heavy
production of stock 5/4 and thicker and the general custom has
developed of cutting the greater part of the log into 6/4 stock. Such
practice means that a large portion of the output is piled in random —
widths and lengths and that extremely wide stock is not uncommon.
Sixteen feet is ordinarily the standard length.
Like most producing sections, the region employs generally a num-
ber of more or less distinctive methods in its air-seasoning practice.
Wide alleys, 16 feet or over, are the rule. The foundations, almost
without exception, have ample height and clearance. A very appre-
ciable amount of thick stock is air seasoned and largely in random
widths. Sixteen-foot box piles are ordinarily used, and the trend is
toward high piles. The standard dimensions of special crossers are
2 by 4 inches. Stock crossers are used largely on the common and
box grades. Although some plants employ adequate spacing between
boards, the interval is often insufficient, particularly in random-
width stock. The single, straight center chimney, 8 to 20 inches
wide, is commonly used in piles of mixed widths.
RESULTS FROM PRESENT PRACTICE
The region as a whole suffers heavy air-seasoning losses, an
appreciable part of which is avoidable. A careful estimate of the
loss, compiled in connection with the studies made in that territory,
indicated, on the basis of a drop of one grade, an average degrade
of 22 per cent for all stock air seasoned. This means an actual
depreciation of $2.20 for each thousand feet. The variation in
degrade between yards was from 9 to 35 per cent. Such losses should
provide ample incentive for improvements in air-seasoning practice.
Blue stain, to which both species of pine are susceptible, is the
major cause of loss. This is to be expected in view of the large cut
of pine and the regional climatic conditions. Degrade from check-
ing is sericus in all species, particularly white fir, and especially
during the summer period. Losses are heaviest in the common and
box grades as a result of the rather general practice of self-crossing
ae stock. Cupping and knot defects also contribute to the regional
osses,
Although not applicable to the specific yard, Figure 8 affords a
fairly good idea of the average drying rates and final moisture con-
tents which can be obtained with present practice. From September
to February a relatively long drying period is necessitated, and
during only seven months of the year will stock in pile come down
to an average moisture content of 15 per cent or less. Ordinarily,
stock air-dry in October, if left on crossers in the yard, will there-
after begin to pick up moisture and by the end of January will
contain 20 per cent or more.
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 51
RECOMMENDATIONS FOR IMPROVEMENT
The major problems for the region as a whole briefly stated are:
(1) The reduction of blue stain, (2) the elimination as far as prac-
ticable of shrinkage defects, (3) faster rate of drying during the
winter season, particularly in the lower part of the pile, and (4)
lower final moisture contents in the inactive drying season. Sug-
gestions for improvement of the general air-seasoning methods to
meet these broad regional problems are as follows:
Sanitary measures and more attention to the reduction of vegeta-
tion in the yard are common needs.
The use of 4-foot or wider spacing between the piles at the sides
should be more generally adopted.
All wood should be piled one layer to the course, other methods
of pile construction more effective than double piling being em-
ployed to avoid excessively rapid drying.
Special crossers, 4 inches in width, should be utilized in piling
8-inch and wider stock of No. 3 common-and-better pine and of No. 2
common-and-better in other woods. The special crossers employed in
this region are usually 2 inches thick, but special crossers 1 inch in
thickness should be used on white fir and Douglas fir, especially in the
upper half of the pile.
More open construction in the lower section of the lumber pile is a
primary requisite for the region. This should be obtained by such
methods as double stickers, horizontal openings at intervals, short
chimneys in separate-width stock, and the flared chimney with
random widths.
The spacing between boards in a course should be at least 4 inches
for separate widths and 4/4 random-width stock; a minimum of 5
inches is advisable for 5/4 and thicker mixed widths.
Last, but of real importance, care in the actual construction of the
individual pile is essential.
REDWOOD REGION
GENERAL CONDITIONS
The great bulk of production in the redwood region is concentrated
within a comparatively narrow strip along the northern coast of
California. Although weather conditions encountered at sea-level
plants differ somewhat from those at yards located farther inland,
about the same climatic characteristics prevail throughout the region.
High atmospheric humidities are present at all seasons of the year
but the temperature extremes are confined within a small range.
The most active drying period is from May to October, but through-
out the rest of the year the mean monthly temperature is always
above 45° F. Such conditions, which are shown graphically in Fig-
ure 9, are conducive to relatively slow seasoning. But as a conse-
quence, liability to depreciation from shrinkage defects is small.
Also some drying is possible at all times of the year. _
Redwood, of course, predominates in the cut of this region, ac-
counting for more than 80 per cent of the production. Douglas fir
is the only other wood of importance, the combined cut of white fir,
spruce, and hemlock constituting less than 3 per cent of the total.
o~_ne- am |. wee
52 DEPARTMENT BULLETIN 1425, U. S. DEPT, OF AGRICULTURE
(Table 1.) It is therefore obvious that blue stain is not a factor in
air seasoning. However, the high green moisture content of the red-
wood, together with the less favorable climatic conditions, makes for
real seasoning difficulties.
Production of boards or 4/4 stock is large in the redwood region,
especially in the common grades, but a big volume of thick “ uppers ”
and shop is also cut and considerable dimension is made. Inch com-
mon is rather generally piled in separate widths. Thick shop and
uppers are ordinarily seasoned in random widths. Probably 60 to
70 per cent of the production is shipped green, owing to the facilities
for water transportation and the absence of the stain danger. As a
result, much stock is simply stored at the plants, little or no attempt
being made to obtain drying.
Drying yards in this region are almost without exception badly
congested, a, condition that could well be avoided where drying is
slow and where a species of high moisture content is involved. This
situation is probably the outgrowth of the practice of shipping green
stock, as well as of a rather common shortage of yard space, and of
the fact that seasoning losses are less obvious and obtrusive than in
regions where stain occurs. Not only are yards crowded, but the
entire air-seasoning practice is ordinarily such as to preclude any-
thing like as rapid drying as is easily possible, even with the unfavor-
able conditions existing. Low foundations are the rule. Drainage
and vegetation in many yards could hardly be worse. The “ random-
length ” type of pile is often used. Wide piles are commonly em-
ployed and sometimes piled two layers to the course. The 4/4
crosser is standard for this region, and frequently an excessive
number are used on each course. Spacing between boards in a
course is generally inadequate, and the use of chimneys in piles of
random-width stock does not follow the best practice. Finally, care-
less or inadequate roofing is a frequent and serious obstacle to rapid
drying.
RESULTS FROM PRESENT PRACTICE
A survey of the depreciation resulting from air seasoning in the
redwood region indicates an actual footage loss of 2.5 per cent which,
very conservatively, means a regional average loss of $1.23 per
thousand feet. Favorable natural conditions, and not air-seasoning
methods, prevent much greater depreciation. But even if the de-
preciation loss does not appear to justify more concern, the cost to
the operators of a drying period of such excessive length as is
necessitated under present practice ought to do so.
Figure 9, which only attempts to picture the average regional
drying situation, clearly indicates unsatisfactory seasoning. Ex-
cept for stock piled in May, June, July, and August, very long
drying periods are required. Also, reasonable final average mois-
ture contents are obtained only from about June 1 to September 30.
Weather conditions and the species concerned are, of course, in part
responsible for such difficulties, but improper practice aggravates
these inherent difficulties unnecessarily.
What does this mean to the industry? ‘In addition to the very
real objections of marketing a product of unsuitable moisture con-
tent, there is a more tangible loss. Careful estimates of the average
air-seasoning in both the redwood and California pine regions will
THE AIR, SEASONING OF WESTERN SOFTWOOD LUMBER 53
illustrate this in a concrete manner. In California the average cost
of carrying the investment in lumber while drying in the yard is
about 32 cents per thousand feet, and the insurance and taxes on this
lumber call for an additional 28 cents per thousand feet or a total of
60 cents. These costs for the redwood region, due to the prolonged
drying period, amount to $2.18 and $0.54, respectively, or a total of
$2.72. This means a cost of $2.12 per thousand in excess of that in
the pine territory. Certainly this alone is a sufficient margin to
justify considerable expense per thousand in improvement of air-
seasoning methods.
A rather usual contention is that the lack of available space makes
crowded yards unavoidable and prohibits the adoption of more open
|
_24e7|_FicToR HOH) DEG
: COMPARATIVE MONTHLY WEATHER COND/7/ONS
AVERAGE DRIVING PELLIDES FOR L4 STUK PULLD 1 LUPECEMT HUWTHE 70 REAL [5 PER CENT HUTTE CUTE
al ee A a ae eS
APLREOVMATE AA OSTURE CONTENT OF THOCHMG (UY LU?-LfPY STICK Be LON TALS.
FER CENT
LZ \MUSTURE CONTENT Z4Z\ ZE\| 22?\ 70O| 78\ /6\ 45 \ 75) S6\77| 7P\ 2
AVERAGE PUCK P OF MIOSTLIAE FEY '}L0CD STOCK AT O1FFERLIVT SLASONS
wool s |+\~|~|-|-|-] -| |e |e |
Fic. 9.—Graphiec air-seasoning chart for the redwood region
PER CEN 7
RELATIVE
H1L14/ 0/7
OF?
TEMPERATURE
c=
——_—/FELATIVE HUMIDITY MONTHLY MEAN
30 <== FEMPERATURE-MONTHLY MEAN
piling. Some plants have very definite limitations to yard extension,
it is true, but even at these plants the possibility of more rapid dry-
ing and consequent faster overturn of stocks will often warrant better
practice. Another defense of current practice is to the effect that,
since only stock piled in the spring and early summer will be dry
enough to ship prior to the next spring, there is little use of better
piling methods. This argument loses weight, however, when it is
considered that the length of the average drying period can be
greatly reduced by improvements in drying practice.
RECOMMENDATIONS FOR IMPROVEMENT
The protracted drying period and unsuitable final moisture con-
tent are of major importance, and reduction of checking and cupping
should not be overlooked. The natural drying influences should be
54 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE
utilized to the greatest possible degree by yard practice which will
afford maximum air movement in both the yard and the lumber
pile. The following improvements in the general regional practice
are suggested :
Yard congestion should be relieved by wider alleys and wider
spacing between piles at the side.
Drainage and vegetation in the yard should receive proper atten-
tion.
Higher foundations are essential.
The use of narrower piles should be thoroughly considered.
All stock should be piled one layer to the course.
The 8/4 special crosser might well be the standard for the region,
as well ag three crossers on 16-foot and shorter stock and four on
stock of greater lengths.
A wider spacing between boards in a course with both separate and
random widths is necessary.
The use of three or more chimneys, or the flared chimney with ex-
ceptionally wide stock, is desirable.
All stock should be roofed in a thorough manner.
The principal steps to reduce checking are elimination, as far as
practicable, of the practice of self-crossing stock and abandonment of
the random-length type of pile. At plant locations where at certain
periods of the year there is liability of checking and cupping, changes
in piling methods should aim primarily to open up the lower part of
the pile.
The adoption of such recommendations may appear to many oper-
ators as necessitating an impracticable expansion of yard space. As
a matter of fact, a large part of the expansion seemingly required is
apparent only. The recommended practice should result in a reduc-
tion of the present seasoning time, thus speeding up turnover to a
point where it would largely, if not entirely, compensate. There are
a few yards in the redwood region where expansion is physically
impossible, but at the others there is no real inability to expand. No
more difficulties exist here than in the California pine region, where
open yards of larger area are already accepted as common practice.
The benefits to the redwood operators in freeing themselves from the
erip of tradition and following the example of other regions in this
respect would be even greater than they have proved to be in the
California pine region.
DOUGLAS FIR REGION
GENERAL CONDITIONS
The Douglas fir region of Oregon and Washington is bounded on
the west by the Pacific Ocean and includes all of these two States
west of the Cascade Mountains. It has a width of 70 to 170 miles
and a length of 500 miles. Because the majority of the mills are
located at the principal harbors, the variation in natural conditions
at the different drying yards is by no means as great as would be
expected in a region of this size. The climatic characteristics of this
producing region are illustrated in Figure 10. Seasonal temperature
fluctuation is relatively small, and mild winters are the rule. Relative
humidities, however, show a marked variation at different periods
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 55
of the year and are responsible for an inactive drying season extend-
ing from about October 1 to April 30. June, July, and August are
the most favorable drying months, but rarely do temperature and
humidity during these months reach such extremes as to cause ex-
cessively rapid drying.
Douglas fir lumber constitutes 80 per cent of the output of this
region. Next in volume is western hemlock, which constitutes 10
per cent of the total. Sitka spruce and western red cedar together
account for 7 per cent. Other softwoods, including the true firs
Beer] aacr oR
COMPRBPATIVE MAONTYILY WEATHER CONOATIONS
PER CLT
ALLATIVE
AILS AA/O/7
BS GO
TEMPLEATUCE
Ze
ACTIVE DRYING SEASON
Behe .
—— AELATIVE HUM/D/ITY-MONTHLY AVERAGE 5 OR BPA.
sm == TEMPERATURE -/4EAN MONTHLY
MWEKAGE PRYING PLRODS FoR G0CK 1 LUFLOLNT NUONTHE SAWERAGCGE WUPIBER OF LAKE
TO RESCH N\4 s
2 LE NG \ o0| 60| s6| 26 | 26 | 20 | 20| |peco|eo| a0
MO/STURE yy
CONTENT '\74 \ ya\ 9o\ G8 \ 45\ BE \ 30 | 30 \ 25|\L9O|\200\/70\20
7 a es Pen
APLROUMATE MUSTURE CONTENT OF THOR} G pL Y ARDY STOCK BY MONTHS
PER CENT
AVERAGE PCKUP OF MUISTURE By EVAR STOCK AT DIFFERENT SEASO/YS
eee ee | Fe) i se) |- | | |? 28
Fic. 10.—Graphic air-seasoning chart for the Douglas fir region
70 REACH
18 FER CLT
VVOVET URE
CONTENT
and Port Orford cedar, make up less than 1 per cent of the cut.
(Table 1.)
Certain characteristics of these species bear on the air-seasoning
practice of the region. Little or no consideration has to be given
to blue stain, either in the seasoning yard or in green shipments
by rail or water. Douglas fir, western red cedar, and Sitka spruce
are species of relatively low moisture content. Western hemlock is
not excessively high.
In considering the extent to which air seasoning is practiced in the
Douglas fir region, markets and the size of the stock cut must be
taken into account. Of the total annual production in the region,
probably a little less than half is shipped to domestic and foreign
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58 DEPARTMENT BULLETIN 1425, U. S. DEPT, OF AGRICULTURE
markets by water, and the bulk of these water-borne shipments, as
well as of the considerable rail shipments, is made up of green lum-
ber. The region, moreover, is an unusually large producer of thick
stock. or sizes thicker than 1 inch. Probably 380 per cent of the
regional cut consists of dimension (2 inches thick), and an additional
20 per cent of planks, small and large structural timbers, squares,
railroad ties, and the like. Less than 20 per cent goes into common
boards.
Only an approximation of the quantity of lumber air seasoned in
the Douglas fir region can be given. Practically all the manufactur-
ing plants are equipped with dry kilns, with the exception of a few
cargo mills, the tie-cutting plants, and the small portable and custom
mills. Hence it is that practically all the clear lumber and a small
proportion of the dimension and common boards, amounting to about
35 per cent of the total lumber cut, is dried in kilns. Fully 50 per
cent of the cut is shipped green, since for the large proportion
shipped by water there is no incentive to reduce the weight of the
lumber through seasoning. Only about 15 per cent of the regional
output is alr seasoned or partially air seasoned, and this consists
chiefly of dimension and common boards.
In the air-seasoning practice of the region the width of the pile
alleys is generally good, but spacing at the rear and at the sides of
the pile is usually inadequate. Foundations, especially in the older
yards, are entirely too low. Although the box and modified-box
types of pile are commonly used, the random-length type is em-
ployed to a large extent, particularly in piling No. 2 and No. 3
common boards and dimension, shiplap, and box grade lumber.
Square, low piles are most frequently found. Practically all stock
is self-crossed. The spacing between boards in a course will average
only about 21% inches and chimneys are little used.
RESULTS FROM PRESENT PRACTICE
Accurate records of air-seasoning depreciation in Douglas fir
common as summarized in Tables 7, 8, and 9, show definitely that
season check and loose knots are the principal causes of degrades.
Season check, which is heaviest during the summer months, is due
principally to the practice of self-crossing, which results not only in
a heavy loss in the stock crossers, but also in an increased loss in the
piled stock because of the crossers. “ Fall-down” from loose knots
is greater in machining than in seasoning, and there is little oppor-
tunity to reduce this defect in seasoning since it is in large measure
due to structural causes. However, all direct seasoning losses for
the region are subject to reduction by reasonable additions to the
piling cost.
|
THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER 59
TABLE 9.—Amount of degrade due to loose knots im 1-inch No. 1 common
Douglas fir
Degrade due to loose knots
Total
Total
Lot No. volume degrade Proportion
ErCen Seasoning | Machining} Total of total
degrade
Board feet Per cent Per cent Per cent Per cent Per cent
Lee set 19, 733 10. 69 2.11 5. 94 8. 05 75. 30
OAS 20° a a rene Dre ca ees US 22, 187 15. 81 3. 89 9. 47 13. 36 84. 50
8h So ee ieee 2 16, 886 17. 06 7. 84 | 8. 34 16.18 94. 84
eS Gly aay) a ae a 22, 795 17. 60 7. 67 9. 08 16275 95.17
Fj ats JERS SW eemenenees A oN) 8 23, 563 8. 47 1. 58 6. 29 7. 87 92. 92
Gi 2 > Bebe Ae ele eo puna oie 13, 200 67. 82 3. 64 | 13. 81 17. 45 25. 73
2 | eee eg SRE ee 15, 216 39. 55 32 11. 04 11. 36 28. 72
i eebees ere e 8, 120 52. 37 3.00 | 24. 48 27. 48 52. 47
po aa 10, 444 34. 37 2. 94 16. 81 19. 75 57. 46
More serious, if indirect, seasoning losses are indicated in Figure
10, which shows that with present practice long seasoning periods are
required for stock piled in the period September to March. It also
shows that during only seven months of the year may suitable mois-
ture contents be obtained. Stock thoroughly air-dry in September
willl pick up moisture rather rapidly until the first of the year, when
it may contain as high as 26 per cent moisture. Existing climatic
conditions are, of course, the primary cause of such results, but much
can be done by way of seasoning practice to minimize these difficulties.
RECOMMENDATIONS FOR IMPROVEMENT
The two major air-seasoning problems of the Douglas fir region
are the reduction of the drying period and the lowering of the final
moisture content of stock. Prevention of checking is also of real
importance. Suggestions for change in regional practice to meet
these problems are as follows:
Improved yard drainage is a rather general need.
Rear alleys should be wider, and greater spacing should be allowed
between the sides of the piles.
A requirement of vital importance is that of higher foundations.
The spacing between boards in a course should be increased, and
gue or more chimneys should be used in piles of random-width
stock.
To prevent the development of season check, stock crossers should
not be employed on select common and better Douglas fir, nor on
No. 1 common over 8 inches in width.
The use of the random-length type of pile should be discontinued.
ORGANIZATION OF THE
UNITED STATES DEPARTMENT OF AGRICULTURE
September 24, 1928
Secretary of Agriculture... 2 W. M. JARDINE.
ASSUSLOIL (SEErClOry 7 Sk eee R. W. DUNLAP.
Dizector of-Seientifie Worlc_= 2 => >= ae A. F. Woops.
Director of Regulatory Work___—___--__--~— — WALTER G. CAMPBELL.
Director of Hxtension____s#--_-__-____+_.__-. C. W. WARBURTON.
Director of Personnel and Business Admin-
iT CHON 2 = ee ee W. W. STocKBERGER.
Prceror of Informemen ee ees NELSON ANTRIM CRAWFORD.
SLES, 1; = Sale 2 I tT Reem ene 28 LE ATES 22 R. W. WILLIAMS.
Wicaiher Bureou. a. a ee CHARLES F. Marvin, Chief.
Burceu of Animal aniustry_ = 2s 2 a JOHN R. MOHLER, Chief.
Bureau of Detry indusiry___ 3 es O. i. REED, Chief.
Bureau of Plant Industry__—_<_—__ __._s.. WILLIAM A. Taytor, Chief.
ORCSE SCTE. fae eB Fee ee ee R. Y. Stuart, Chief.
Bureau of Chemistry and Soils_____________- H. G. Knicut, Chief.
Burcosu Of intomogye 2 eee C. L, Martatt, Chief.
Paureul. 07 Biological: Survey. rae PauL G. REDINGTON, Chief.
FUrca Of Pte hoUds. >= Ss eee THomMAS H. MACDONALD, Chief.
Bureau of Agricultural Heonomics____----~--- Nits A. OLsEn, Chief.
Bureau of Home EHconomics_____._-__-_--—_-- Louise STANLEY, Chief.
Plant Quarantine and Control Administra-
(257) (eS ES a a Ee OT ieee es Sh C. L. Marwiatt, Chief.
Grain Futures Administration__________-_-__- J. W. T. Duvet, Chief.
Food, Drug, ané Insecticide Administration.. WALTER G. CAMPBELL, Director of
Regulatory Work, in Charge.
_Office of Experiment Stations_______-_-_-__~- BE. W. ALLEN, Chief.
Office of Cooperative Extension Work________. C. B. SmirH, Chief.
PBA p eee Sis Peat. aU EES |: 2 CLARIBEL R. BARNETT, Librarian.
This bulletin is a contribution from
MORCSE SCrULCCte nee Se net eee oe R. Y. Stuart, Forester.
ES TALICH: hy DRRCSOILT Clie ® 22) <Oe _ EARLE H. Cuiapp, Assistant For-
ester, in Charge.
Office of Forest Products_—____~-- > H. S. Betts, in Charge.
60
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