Preservative treatment of fence-posts

PRESERVATIVE TREATMENT OF FENCE-POSTS

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DEPARTMENT OF THE' I Is] TEillG R

FORESTRY BRANCH— CIRCULAR No. 6.

If. IT. CAMPBELL, Director of Forestry.

RESERVATIVE TREATMENT
OF FENCE-POSTS

R. G. LEWIS, B. Sc. F.

OTTAWA

GOVERNMENT PRINTING BUREAU
1913

DEPARTMENT OF T.ES I^TiEKI

FORESTRY BRANCH— CIRCULAR No. 6.

E. H. CAMPBELL, Director of Forestry.

PRESERVATIVE TREATMENT
OF FENCE-POSTS

R. G. LEWIS, B. Sc. F.

OTTAWA

GOVERNMENT PRINTING B U S E A TJ
1913

401 10—1

Agric. -Forestry. Main Library

CONTENTS.

PAGE.
Introduction « 5

Choice of Preservative 5

Choice of Material 8

Preparation of Material . . . * 8

General Object of Treatment • 8

Brush Method 9

Open-tank Method ' 9

ILLUSTRATIONS.

Piling Posts for Seasoning (Fig. 1) 6, 7

Methods of Bevelling the Tops of Posts (Fig. 2) 6, 7

Home-made Plant for Treating Fence-posts (Fig. 3) 10

Heating Tank (Fig. 4) 6, 7

Cooling Tank (Fig. 5) 6, 7

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PRESERVATIVE TREATMENT OF FENCE-POSTS.

The supply of durable woods for fence-posts in Canada is rapidly decreasing, and
with this decrease comes the inevitable increase in cost and reduction in quality and
size of material. Cedar is, at present, the most abundant native wood that is at all
durable in contact with moist soil. The supply of posts of this material is rapidly
nearing exhaustion. Oak and chestnut are durable, but these woods are so scarce and
so valuable for other purposes that they are not used extensively for posts.

Canada, however, is fortunate in possessing an abundance of the less durable woods
such as poplar, jack pine, spruce, balsam fir and willow which are more readily treated
by preservatives than the denser hardwoods.

Where the cost of cedar and other durable woods becomes excessive, the use of
inferior woods becomes necessary. Where posts of these woods decay rapidly, the cost
of replacing them becomes an expense, no matter how cheap the material may have
been. It is, then, necessary to calculate the actual saving that could be accomplished
by treating such material with a preservative of some sort to prevent or retard decay.

Before deciding on such an action it is necessary to consider all the factors that
enter into the cost of fence maintenance.

These include the first cost of the post, the cost of peeling and seasoning, the cost
of transporting from the source of supply to the place of setting arid the cost of setting
the post; in the case of treated posts, the cost of treatment must also be included. In
order to get a fair comparison of treated and untreated posts, all these different items
must be added, and the total cost divided by the number of years the pole will last in
order to arrive, roughly, at the cost per year (annual cost) for the post.

With untreated material, to the initial cost of the post is to be added the cost of
seasoning, transporting from the source of supply to the farm and putting the post in
place.

With treated material the initial cost is usually lower, as inferior species can be
used. The cost of transportation is usually lower, as local supplies are available. The
cost of peeling and seasoning may be higher, as posts must be peeled and well seasoned
before they can be properly treated. The cost of treatment will be the most important
item and will depend on the preservative used and the treatment adopted. The cost
of placing the post will be less as an annual charge because the post will last longer and
will not need to be replaced so often. All these cost items can then be considered
in relation to the increased life that the treatment will cause. The annual cost of each
post will be found to be much less for treated material than for untreated in the
majority of cases.

Preservative treatment of fence-posts has been experimented with under a multi-
tude of different conditions, and the results recorded. A summary of these results indi-
cates that an enormous saving in actual dollars and cents can be accomplished by the
use of proper preservative treatment.

CHOICE OF PRESERVATIVE.

Experience has shown that creosote, or deal oil of coal tar (or some of the patent
preservatives with this substance as their base) is the most satisfactory preservative
for wood which is to be used in contact with moisture. There are two primary reasons

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8 ^ FORESTRY BRANCTl" CIRCULAR NO. 6.

for this. Creosote is a chemical poison to the different organisms or fungi that cause
decay in wood and also to the different insects that destroy it. Creosote is a heavy oil,
insoluble in water. If it can be forced into the substance of seasoned wood it prevents
the further absortion of water. Moisture and air are necessary for the growth of fungi
and if wood can be kept dry it will last indefinitely.

There are many substances such as zinc chloride, mercuric chloride, copper sul-
phate and others that are poisonous to fungi and insects, but these are all soluble in
water and when used as wood-preservatives must be dissolved in water. "Whenever the
wood so treated comes into contact with moisture, the preservative will dissolve again
and leach out, leaving the wood liable to attack by the agents of decay.

Creosote is a by-product obtained in the manufacture of coal gas and is a more or
less variable substance. The denser the oil, the more difficult it is to force it into the
wood, but the less likely it is to evaporate, either during the process or after it has pene-
trated the wood substance. The lighter the oil the deeper the penetration, but the
higher the loss by evaporation.

The oil can be obtained in almost any large city where coal gas is manufactured,
and costs in Canada from 10 to 25 cents a gallon, depending on quality, density, trans-
portation charges and quantity purchased.

CHOICE OF MATERIAL.

The choice of material to be treated will depend largely on local conditions of
supply. In the Maritime Provinces the most economical woods for treatment will prob-
ably be spruce, hemlock and balsam fir ; in Quebec and Ontario, spruce, hemlock, balsam
fir and jack pine; in the Prairie Provinces, poplar, jack pine, spruce and willow; in
British Columbia, lodgepole pine, western yellow pine, and poplar. One of the chief
advantages of preservative treatment is that it makes possible the use of the cheaper
class of local woods and the choice of material will depend on the initial cost and the
cost of treatment of such woods.

PREPARATION OF MATERIAL.

Whatever material is chosen for fence-posts a thorough seasoning is a primary
necessity. The posts should be cut in the spring as soon after the buds begin to swell
as possible. The bark «an then be removed most readily. Posts should be carefully
peeled, and special care taken to remove the thin inner bark, or bast, as this, if left,
prevents the absorption of the preservative.

Figure 1 shows a method of piling posts for seasoning which allows a free circula-
tion of air. They are placed in alternate tiers of three and seven posts with about
fifty in a pile and the piles should be at least ten feet apart. Posts cut and peeled in
the spring and allowed to season through the summer are ready for treatment in the
early autumn.

Bound posts are preferable to split material as the preservative will, in the majority
of cases, penetrate only the sapwood.

The top of each post should be bevelled off as shown in figure 2 to shed the rain and
prevent the top becoming water-soaked.

GENERAL OBJECT OF TREATMENT.

The general object of the treatment is to obtain as deep a penetration of creosote
into the cells of the wood as possible with the least quantity of preservative and the
least loss from evaporation during the process.

PRESERVATIVE TREATMENT OF FENCE POSTS. 9

THE BRUSH METHOD.

This is the least expensive method of applying creosote to fence-posts and is to be
recommended only on account of its cheapness.

Give the butts of the posts at least three coats of hot creosote with an ordinary
brush. Heat the oil to boiling and keep it hot while applying each coat. Fill all cracks
and checks carefully. Allow each coat to be absorbed before applying another. Stand
each post on end, butt upwards, while drying, in order to allow any surface oil to run
toward the top of the post. If possible, do the work in warm weather and in the sun.
If the oil cools too quickly, or if the posts are cold, the oil will congeal on the surface
and will not penetrate into the wood cells. If desired, a coat of oil can be applied to
the entire post to prevent decay of the upper part. As a rule, it is necessary to paint
only the butt of each post up to a point at. least six inches above the ground-line, as
this is the part most liable to decay. This treatment usually results in a penetration
of about one quarter (i) of an inch of creosote of ordinary density. This should add
at least ten years to the life of a post of a non-durable wood such as poplar, balsam fir
or spruce.

THE OPEN-TANK METHOD.

This is a more satisfactory method than that described previously, but it neces-
sitates a more or less costly plant.

The theory of the method is a simple one. The posts are heated in a hot bath of
creosote which expands the air in the wood-cells and turns a part of the moisture in
the wood into steam. This expansion forces out a certain part of the air and water in
the wood. The posts' are then placed in a cooling tank, or allowed to cool in the heat-
ing bath, and the contraction of the air remaining in the cells and the condensation of
the steam produces" a partial vacuum that draws a certain quantity of preservative into
the cells of the wood.

The vessel or vessels used, the time taken in heating and in cooling and the details
of the method generally will depend on the judgment of the operator and the cost of
apparatus.

Figure 3 shows an inexpensive " open-tank " plant that can be made on any farm.
It consists of a tight barrel, three lengths of piping and the necessary couplings. Place
a charge of posts in the barrel and pour in creosote until the upper arm of the piping is
below the surface of the oil. Build a fire below the lower arm of the piping as shown in
the sketch. Take care to screen the barrel from the fire, as the oil is very inflammable
and can be easily ignited by a chance flame or spark. The heating will set up a cur-
rent, and will gradually raise the temperature of the oil in the barrel to boiling point
and keep it at this temperature. Do not allow the oil to reach a higher temperature
than 220 °F., or the loss due to evaporation will be excessive. This loss will vary from
ten to twenty per cent in any case, depending on the density of the creosote. Leave the
posts in this bath until no more bubbles rise to the surface of the oil. This time will
vary according to the nature of the wood used and the extent of its previous seasoning
and should run from one to six hours. The time taken will vary under different con-
ditions and should depend on the judgment of the operator. A few trial charges of
posts will show the most economical time.

After the heating is completed, withdraw the fire and allow the oil to cool. Leave
the posts in the cold oil from half an hour to four hours, or until a sufficient penetra-
tion has been obtained. This can be determined by trial only as different conditions
will have different effects on the result. After the cooling is completed allow the posts
to drain off by placing them in an empty barrel, butts upward. The excess of oil can
then be collected and used over again.

This method permits of many variations in procedure and in apparatus used. The
posts may be removed from the heating bath at the completion of the heating and

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k 'FORESTRY "BRANCH 'CIRCULAR NO. 6.

PRESERVATIVE TR^A^^Tr^^T* b^P^'C^O^'DS. 11

placed in a separate barrel containing cool creosote and left in this barrel until the
necessary penetration is obtained. The heating barrel can then be recharged imme-
diately, and the process made a continuous one with little or no loss of time. A wooden
tank long enough to hold the posts lying on their sides completely submerged can be
used as a cold bath. The butts, having been heated the most, will absorb the most
creosote and the tops will take up a comparatively small quantity, producing ideal con-
ditions to withstand decay. Some of the more perishable woods such as poplar, willow,
maple and scrub oak require this additional top treatment. The same result may be
obtained by applying the open-tank method to the butts and a brush application to the
top parts of the post.

The above apparatus is quite good enough for a small number of posts. Where
large quantities are to be treated the plant should be of a more permanent nature. The
wooden barrel will leak and the joints cannot be kept absolutely tight. A galvanized
iron barrel or tank can be substituted for the wooden barrel and these difficulties over-
come. There is a considerable waste of heat and a danger of igniting the oil in the
use of the open fire. If a heavy metal tank is used in place of the wooden or galvanized
iron barrel, a fire can be built directly beneath it and the fire kept under control by
building a stone or brick fireplace with a stove-pipe chimney. Where steam is avail-
able, galvanized iron can be used and coils can be placed in the bottom of the tank to
heat the creosote. This removes the fire danger and keeps the oil at a constant tem-
perature with a reduced loss due to evaporation. Figures 4 and 5 show a complete open-
tank apparatus with steam connections. The piping in the cooling tank is used to
admit steam in cold weather when there is a danger of the creosote solidifying. Many
modifications of this apparatus and of the method outlined will suggest themselves to
the operator who can adapt them to his requirements.

MAR 23 1931

APR 2 41953 Li

YD 02930

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