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Full text of "10-year paint tests on weathered galvanized roofing"

630.7 
I6b 

no. 676 
cop. 8 



UNIVERSITY OF 

ILLINOIS LIBRARY 

AT URBANA-CHAMPAIGN 

AGRICULTURE 



^ 



= u 



BULLETIN 676 




10 -YEAR PAINT 
WEATHERED GALVANIZED ROOFING 



By A. J. Muehling and J. O. Curtis 



UNIVERSITY OF ILLINOIS 
AGRICULTURAL EXPERIMENT STATION 



Urbana, Illinois August, 1961 

Publications in the Bulletin series report the results of investigations made 
or sponsored by the Experiment Station 



' 






CONTENTS 

DESCRIPTION OF TESTS 6 

Application of Paints 6 

Inspections 13 

Criteria for Evaluating Tests 13 

TEST RESULTS 15 

Performance of Paint Systems 15 

Effect of Exposure 20 

Effect of Original Condition of Sheet 22 

Effect of Wire Brushing Sheets Before Applying Paint 23 

SUMMARY 26 

LITERATURE CITATIONS. . . .27 



COVER PHOTO fhe 150-foot corn crib on which the paint study 
was conducted (south side after application of first coat of paint). 




This bulletin was prepared by A. J. Muehling and J. O. 
Curtis, Assistant Professors of Agricultural Engineering. 

The research reported here was initiated by R. W. 
Whitaker, formerly Instructor of Agricultural Engineering, 
now Director of Agricultural Research, A. O. Smith Cor- 
poration, Milwaukee, under the direction of D. G. Carter, 
Professor of Agricultural Engineering. 

For several years, inspections of the test panels were 
conducted in the Department by H. L. Wakeland, now 
Assistant Dean of the College of Engineering, University 
of Illinois. 

Funds for this project were provided in part by the 
American Zinc Institute and the Aluminum Company of 
America. 



GALVANIZED METAL SHEETS ARE STEEL SHEETS that have been COated 
with zinc to prevent the steel from rusting. As this zinc coating 
deteriorates through weathering, the steel becomes exposed and begins 
to rust. Besides being unsightly, rusting reduces the life of the roofing. 

Galvanized metal roofing and siding are used extensively on farm 
buildings. A 1941-1942 survey (8)* by the American Zinc Institute 
in 36 states east of the Rocky mountains showed that one-third of all 
farm buildings had galvanized steel roofs. More than one-fourth of 
these roofs were rusty. According to a 1944-1954 survey (7), the 
roofs of about one-half of all Illinois farm buildings were made of 
galvanized steel. About 50 percent of these roofs showed signs of rust. 

The application of protective paints is one of the least expensive 
means of preventing rusting of galvanized metal sheets, provided that 
the paint is chosen carefully. Painting also makes the building more 
attractive and can reduce roof temperatures by reflection. 

Paints vary in their ability to adhere to metals, to withstand ex- 
posure, and to prevent rusting. Manufacturers' tests indicate the rela- 
tive ability of paints to protect metal from corrosion. However, the 
final evaluation of a particular paint can be obtained only by direct 
exposure to the elements. According to several authorities (5, 10) 
accelerated laboratory tests do not predict the service life of a paint, 
and the final trial should be under field conditions. 

In 1932, the American Zinc Institute established tests of paints on 
galvanized metal roofs at Donnellson, Illinois. These tests are usually 
referred to as the Harwood Tests. In 1948, test data covering 16 years 
were turned over to the Department of Agricultural Engineering at 
the University of Illinois. The data were analyzed and the results 
published (3,4). 

After studying the results of the Harwood Tests and reviewing 
other technical literature on paint for metal roofs, the University of 



* This number and similar numbers in parentheses refer to the literature 
citations on page 27. 



6 BULLETIN NO. 676 

Illinois Department of Agricultural Engineering initiated a new series 
of paint tests in June, 1949. This project was supported in part with 
funds supplied by the American Zinc Institute and the Aluminum 
Company of America. 

The objective of these tests was to expand the knowledge gained 
from the Harwood Tests. Information was sought concerning (a) the 
durability of metallic zinc paints for priming and finish coats on rusty 
galvanized metal roofing; (b) the durability of aluminum paints as 
finish coats over various primers; and (c) the value of wire brushing 
the rusty surface before painting. 

The roof of a 150-foot crib on one of the University-owned Aller- 
ton farms near Monticello, Illinois, was chosen for the tests (see 
cover photo). The rural location corresponded to the least severe 
ordinary exposure condition, according to the classification of atmos- 
pheric types used by the American Society for Testing Materials (11). 
The condition of the galvanized sheets on this roof did not vary as 
much as the condition of the sheets used in the Harwood Tests. Much 
of the metal was quite rusty. A trace of black asphalt paint remained 
on most sheets from a previous painting. These surface conditions were 
as severe as one would be likely to encounter in farm buildings. 

DESCRIPTION OF TESTS 

Application of Paints 

Each panel was composed of corrugated metal sheets approxi- 
mately 2 feet wide and extending up one side of the crib and down the 
other. This arrangement gave a north and south exposure for each 
panel. Before painting, all panels were renailed where needed, and 
the entire roof was brushed with a broom to remove all loose foreign 
material. A three-foot strip of roof was wire brushed across the 
northern exposure of panels 46 through 81 to evaluate the practice of 
wire brushing a rusty galvanized sheet before painting. 

Twenty-three paints from 11 manufacturers were hand-sprayed on 
the test panels in 7 one-coat and 34 two-coat applications. Replications 
were made of all but two panels (panels 11 and 16). In addition to 
giving better test data, these replications provided some insurance 
against a complete loss of record in the event that some of the sheets 
were blown off the roof. Fig. 1 shows the numbered panels on the crib 
and lists the paint combinations that were tested. The compositions of 
the paints as reported by the manufacturers are listed in Table 1. 



FIRST COAT 

1 GRAY MZP (SOYBEAN OIL) 

2 GRAY MZP (SOYBEAN OIL) 

3 ZINC CHROMATE PRIMER 

4 ZINC CHROMATE-IRON OXIDE 

5 RED LEAD (LINSEED OIL) 

6 WHITE LEAD 

7 RED MZP 

8 RED MZP 

9 IRON OXIDE (RED RUST-RESISTING PAINT) 

10 GREEN MZP 

11 GREEN MZP 

12 GREEN AUTO ENAMEL 

13 GRAY MZP (LINSEED OIL) 

14 RED LEAD (LINSEED OIL) 

15 RED LEAD (SEMI-QUICK-DRYING VEHICLE) 

16 ZINC CHROMATE-IRON OXIDE 

17 ZINC CHROMATE PRIMER 

18 ALUMINUM, GENERAL PURPOSE (I) 

19 ALUMINUM, GENERAL PURPOSE (I) 

20 GRAY MZP (SOYBEAN OIL) 

21 GRAY MZP (SOYBEAN OIL) 

22 GRAY MZP (SOYBEAN OIL) 

23 GRAY MZP (LINSEED OIL) 

24 GRAY MZP PRIMER 

25 RED LEAD OXIDE (LINSEED OIL) 

26 GRAY MZP PRIMER 

27 ALUMINUM (RUST-RESISTING VEHICLE) 

28 ALUMINUM (RUST-RESISTING VEHICLE) 

29 RED LEAD OXIDE (LINSEED OIL) 

30 GRAY MZP (SOYBEAN OIL) 

31 GRAY MZP (SOYBEAN OIL) 

32 ASPHALT ALUMINUM 

33 ASPHALT ALUMINUM 

34 ASBESTOS ASPHALT 

35 ALUMINUM, FOR METAL & MASONRY (I) 

36 ALUMINUM, FOR METAL & MASONRY (I) 

37 ALUMINUM, SPECIAL 

38 GRAY MZP (SOYBEAN OIL) 

39 GRAY MZP (SOYBEAN OIL) 

40 GRAY MZP (SOYBEAN OIL) 

41 SPECIAL RED PRIMER (NORTH ONLY) 

42 GRAY MZP (SOYBEAN OIL) 

43 GRAY MZP (SOYBEAN OIL) 

44 ZINC CHROMATE PRIMER 

45 ZINC CHROMATE-IRON OXIDE 

46 RED LEAD (LINSEED OIL) 

47 WHITE LEAD 

48 RED MZP 

49 RED MZP 

50 IRON OXIDE (RED RUST-RESISTING PAINT) 

51 GREEN MZP 

52 GREEN MZP 

53 GREEN AUTO ENAMEL 

54 GREEN MZP (LINSEED OIL) 

55 RED LEAD (LINSEED OIL) 

56 RED LEAD (SEMI-QUICK-DRYING VEHICLE) 

57 SPECIAL RED PRIMER 

58 ZINC CHROMATE PRIMER 

59 ALUMINUM, GENERAL PURPOSE (I) 

60 ALUMINUM, GENERAL PURPOSE (I) 

61 GRAY MZP (SOYBEAN OIL) 

62 GRAY MZP (SOYBEAN OIL) 

63 GRAY MZP (SOYBEAN OIL) 

64 GRAY MZP (LINSEED OIL) 

65 GRAY MZP PRIMER 

66 RED LEAD OXIDE (LINSEED OIL) 

67 GRAY MZP PRIMER 

68 ALUMINUM (RUST-RESISTING VEHICLE) 

69 ALUMINUM (RUST-RESISTING VEHICLE) 

70 RED LEAD OXIDE (LINSEED OIL) 

71 GRAY MZP (SOYBEAN OIL) 

72 GRAY MZP (SOYBEAN OIL) 

73 ASPHALT ALUMINUM 

74 ASPHALT ALUMINUM 

75 ASBESTOS ASPHALT 

76 ALUMINUM, FOR METAL & MASONRY (I) 

77 ALUMINUM, FOR METAL & MASONRY (I) 

78 ALUMINUM, SPECIAL 

79 GRAY MZP (SOYBEAN OIL) 

80 GRAY MZP (SOYBEAN OIL) 

81 GRAY MZP (SOYBEAN OIL) 



SECOND COAT 

GRAPHITE 

RED MZP 

RED MZP 

RED MZP 

RED MZP 

RED MZP 

RED MZP 

NONE 

IRON OXIDE (RED RUST-RESISTING PAINT) 

NONE 

GREEN AUTO ENAMEL 

GREEN MZP 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

NONE 

ALUMINUM, GENERAL PURPOSE (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, GENERAL PURPOSE (II) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM, GENERAL PURPOSE (II) 

NONE 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM, FOR METAL & MASONRY (II) 

ALUMINUM, FOR METAL & MASONRY (II) 

ASPHALT ALUMINUM 

ASPHALT ALUMINUM 

NONE 

ASPHALT ALUMINUM 

NONE 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, SPECIAL 

ALUMINUM, GENERAL PURPOSE (I) 

NONE 

GRAY MZP (SOYBEAN OIL) 

GRAY MZP (SOYBEAN OIL) (NORTH ONLY) 

GRAPHITE 

RED MZP 

RED MZP 

RED MZP 

RED MZP 

RED MZP 

RED MZP 

NONE 

IRON OXIDE (RED RUST-RESISTING PAINT) 

NONE 

GREEN MZP 

GREEN MZP 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, FOR MFTAL & MASONRY (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

NONE 

ALUMINUM, GENERAL PURPOSE (I) 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, GENERAL PURPOSE (II) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM, GENERAL PURPOSE (II) 

NONE 

ALUMINUM (RUST-RESISTING VEHICLE) 

ALUMINUM, FOR METAL & MASONRY (II) 

ALUMINUM, FOR METAL & MASONRY (II) 

ASPHALT ALUMINUM 

ASPHALT ALUMINUM 

NONE 

ASPHALT ALUMINUM 

NONE 

ALUMINUM, FOR METAL & MASONRY (I) 

ALUMINUM, SPECIAL 

ALUMINUM, GENERAL PURPOSE (I) 

NONE 

GRAY MZP (SOYBEAN OIL) 



Paint treatment for each panel of the corn-crib roof used in the tests. (Fig. 1 ) 



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[August, 



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796J] 



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10 BULLETIN NO. 676 [August, 

ASTM standards D 1014-51 (11) was followed as closely as pos- 
sible when setting up the test procedure. Singleton (9) states that 
when making paint tests, the description of a painting system must 
include at least three items: (a) the condition of the steel surface 
when it is painted, (b) the paint composition, and (c) the thickness 
of paint or amount of paint used on a given area. 

Excellent colored slides showing the original condition of the panels 
were taken before the tests began. These slides were studied and the 
amount of rust on each panel was recorded (see pages 16 to 18). The 
condition of the panels before painting can be seen in Fig. 2. 

Paint was hand-sprayed on the panels in consecutive order, start- 
ing with the first panel on the west end of the building. All paint was 
applied according to the manufacturers' directions by the same person 
using the same equipment. 

The paint coatings were applied with a small (0.203 gallon) De- 
Vilbiss pressure cup unit. An aluminum shield was used to prevent 
the spray from blowing to adjacent panels (Fig. 3). The sprayer cup 
was cleaned after each application except when the same paint was 
applied to successive panels. Panels that were to have the same paint 
were grouped together to reduce the time and labor required for wash- 
ing the cup and maneuvering the shield. 

Table 2 shows the amount of paint applied to each panel, weight 
per gallon, and the amount of coverage in square feet per gallon of 
each paint used. The values from Table 2 were determined by the 
following procedure: 

1. The cup was filled to the 0.203-gallon capacity and weighed 
before the test panel was painted. 

2. After the panel was painted, the weight of the cup was recorded. 

3. The weight of the cup was subtracted from the full weight to 
obtain the pounds of paint applied. 

4. Weight per gallon was calculated from the full weight of the 
cup, the known empty weight of the cup unit (3.43 pounds), and the 
known capacity of the cup (0.203 gallon). 

Full weight minus empty weight (3.43 pounds) equals actual 

weight of 0.203 gallon of paint. 

Weight per gallon equals 1/0.203 times actual weight of 0.203 

gallon of paint. 

The weight per gallon for a given paint sometimes varied slightly 
because of variation in mixing and in the quantity of thinner used (if 
any) . See footnote b under Table 2 for paints thinned. 



?96J] 



PAINT TESTS ON GALVANIZED ROOFING 



11 




North side of crib before painting. The one-third of the roof at the left (Panels 46 through 
81) was 100 percent rusty. (Fig. 2) 

5. The gallons used per panel were calculated by dividing the 
weight of paint used per panel by the weight per gallon. 

6. The actual areas for each panel were measured. 

The coverage in square feet per gallon was calculated by dividing 
the panel area by the gallons used on the panel. 

When the same paint was applied to successive panels, they were 
painted as a single unit and separate panel calculations were not made. 




An aluminum shield was used to prevent spray from blowing to adjacent panels. (Fig. 3) 



12 



BULLETIN NO. 676 



[August, 



Table 2. Area of Panels, Quantities of Paint Used, and Paint Coverage 



Panel 
No. 


Panel 
area 
(square 
feet) 


First coat 


Second coat 


Paint 
No. 


Amount 
of paint 
used 
(pounds) 


Weight Coverage 
per (square 
gallon feet per 
(pounds) gallon) 


Paint 
No. 


Amount 
of paint 
used 
(pounds) 


Weight 
per 
gallon 
(pounds) 


Coverage 

(square 
feet per 
gallon) 


1 


. 80.4 


1 
1 
4 
5 
6 
7 
3 
3 
8 
9 
9 
10 
11 
6 
13 
5 
4 
14 
14 
1 
1 
1 
11 
16 
18 
16 
17 
17 
18 
1 
1 
20 
20 
21 
12 
12 
22 
1 
1 
1 

23 
1 
1 
4 
5 
6 
7 
3 
3 
8 
9 
9 
10 
11 
6 


3.48 
3.02 
2.60 
2.08 
5.25 
3.45 
2.88 
2.66 
2.39 
4.01 
4.12 
2.25 
4.79 
7.30 
4.93 
2.58 
4.38 
1.47 
1.47 
4.90 
4.90 
4.90 
4.48 
4.25 
2.57 
4.33 
1.31 
1.31 
3.01 
3.83 
3.83 
1.22 
1.22 
7 pints 
1.32 
1.32 
1.03 
3.55 
3.50 
3.19 
0.81 
3.36 
3.55 
2.16 
2.26 
7.52 
4.59 
3.36 
3.36 
2.72 
4.20 
4.20 
2.24 
4.90 
6.00 


22.0 
22.0 
14.4 
11.4 
31.1 
18.6 
16.2 
16.2 
11.7 
17.7 
17.7 
8.1 
25.0 
28.2 
24.2 
11.5 
14.5 
7.7 
7.7 
22.6 
22.6 
22.6 
24.3 
24.3 
13.3 
24.5 
8.1 
8.1 
13.3 
22.5 
22.5 
8.1 
8.1 
unknown 
8.5 
8.5 
7.7 
23.5 
23.5 
23.5 
9.4 
23.5 
23.5 
14.5 
12.6 
38.6 
22.3 
16.2 
16.2 
12.1 
23.5 
23.5 
8.6 
25.9 
35.6 


510 

510 
410 
405 
425 
390 
415 
415 
325 
315 
315 
270 
405 
290 
370 
340 
250 
395 
395 
350 
350 
350 
410 
390 
345 
405 
470 
470 
335 
445 
445 
505 
505 
85 
490 
490 
565 
505 
505 
505 
385 
505 
505 
510 
425 
390 
370 
365 
365 
340 
425 
425 
290 
400 
435 


2 
3 
3 
3 
3 
3 
3 

8 

10 
9 
12 
12 
12 
12 
12 

14 
12 
15 
17 
17 
17 
17 
15 

17 
19 
19 
20 
20 

20 

12 
22 
14 

1 
1 
2 
3 
3 
3 
3 
3 
3 

8 

9 
9 
12 
12 


3.06 
2.89 
3.07 
3.07 
2.99 
2.98 
3.07 


11.6 

17.7 
17.7 
17.7 
17.7 
17.7 
17.7 


305 

425 
425 
425 
425 
425 
425 


2 


... 69.8 


3 


... 74.0 


4 


... 74.0 


5b 


... 72.2 


6. . 


71.9 


7 


74.0 


8 


... 68.4 


9 


. . . 66.6 


1.95 


12.0 


410 


10 


. . . 71 .8 


11 


. . 74.0 


2.25 
2.35 
1 .50 
1 .45 
1.45 
1.45 
1.45 


8.3 

18.7 
7.9 
7.9 
7.9 
7.9 
7.9 


275 
600 
410 
410 
410 
410 
410 


12 


... 76.0 


13 . .. 


78.2 


14 b 


... 76.0 


15 


... 76.0 


16 b 


76.0 


17 


.. 76.0 


18 


... 76.0 


19 


76.0 


1.40 
1.00 
1.10 
1.50 
1.50 
1.35 
1.32 
1.10 


7.9 
7.9 
7.6 
8.1 

8.1 
8.1 
8.1 
7.4 


430 
600 
525 
410 
410 
410 
410 
480 


20 


... 76.0 


21 


... 76.0 


22 


... 76.0 


23 


76.0 


24 


.. 68.4 


25 


... 66.6 


26. . 


. 71.8 


27 


. 76.0 


28 


... 76.0 


1.40 
1.38 
1.38 
1.20 
1.20 


7.6 
8.6 
8.6 
8.3 
8.3 


415 

475 
475 
525 
525 


29 


... 76.0 


30 


. 76.0 


31 


.. 76.0 


32 


... 76.0 


33 


76 


34 


. 76.0 


1.20 


8.3 


525 


35 


... 76.0 


36... 


76.0 


1.30 
1.35 
1.35 


8.8 
8.3 
8.3 


515 
465 
465 


37 


76 


38 


76.0 


39 


... 75.2 


40 


68 4 


4.00 
1.95 
2.80 
2.86 
2.86 
2.86 
2.86 
2.86 
2.86 


23.8 
23.8 
11.3 
18.4 
18.4 
18.4 
18.4 
18.4 
18.4 


405 
405 
290 
490 
490 
490 
490 
490 
490 


41... 


. 33.3 


42 


.. 72.3 


43 


... 76.0 


44 


76 


45 b 


... 76.0 


46>>... 


76.0 


47 


... 76.0 


48 


76 


49 b 


... 76.0 


50 . . 


76 


2.60 


13.5 


395 


51. . 


76 


52 


... 76.0 


2.95 
2.95 
1.35 
1.30 


20.9 
20.9 
8.6 
8.6 


540 
540 
485 
485 


53. . 


... 76.0 


54. . 


76 


55>> 


... 73.5 







A detailed description of the paints is given in Table 1. 
b The following paints were thinned to obtain better spraying consistency: 
Panel 5 Red lead (linseed oil) 12 ounces of turpentine added to 9.08 pounds of 

red lead. 
Panel 14 Red lead (linseed oil) 2 ounces of turpentine added to 7.70 pounds of 

red lead. Mixed more thoroughly than for Panel 5. 
Panels 16 and 45 Zinc chromate-iron oxide 3 ounces of turpentine added to 5.77 

pounds of paint. 
Panels 46 and 55 Red lead (linseed oil) 6yi ounces of turpentine added to 18.5 

pounds of paint. About 5 ounces of linseed oil added to paint for Panel 55. 
Panel 49 Red MZP 1 ounce of turpentine added to 1 cup of paint. 
c Only the north side of Panel 41 was painted. A new galvanized sheet was placed on the 
southern exposure before the paint tests started. 



J96JJ 



PAINT TESTS ON GALVANIZED ROOFING 



Table 2. Concluded 



13 



Panel 

No. 


Panel 
area 
(square 
feet) 


First coat 


Second coat 


Paint 
No. 


Amount 
of paint 
used 
(pounds) 


Weight Coverage 
per (square 
gallon feet per 
(pounds) gallon) 


Amount 
Paint of paint 
No. used 
(pounds) 


Weight 
per 
gallon 
(pounds) 


Coverage 

(scjuaic 
feet per 
gallon) 


56 . 


. 66.6 


13 
23 
4 
14 
14 
1 
1 
1 
11 
16 
18 
16 
17 
17 
18 
1 
1 
20 
20 
21 
12 
12 
22 
1 
1 
1 


4.90 
1.40 
2.55 
1 .20 
1.20 
3.32 
3.32 
3.32 
4.25 
4.45 
2.65 
4.25 
1.12 
1.12 
3.55 
3.70 
3.34 
1.14 
1 .26 
7 pints 
1.30 
1 .30 
1.00 
3.70 
3.70 
4.00 


25.7 
8.6 
14.4 
8.0 
8.0 
23.5 
23.5 
23.5 
26.7 
25.2 
13.4 
25.7 
8.7 
8.7 
13.7 
24.1 
24.1 
8.6 
8.6 
unknown 
8.5 
8.5 
8.2 
24.6 
24.6 
24.6 


350 
415 
420 
505 
505 
535 
535 
535 
480 
430 
385 
460 
590 
590 
295 
480 
480 
500 
500 
85 
485 
485 
625 
505 
505 
505 


12 
12 
12 

14 
12 
15 
17 
17 
17 
17 
15 

17 
19 
19 
20 
20 

20 

12 
22 
14 

1 ' 


.18 
.20 
.32 

'.45 
.25 
.50 
.29 
.29 
.29 
.29 
.30 


8.6 
8.6 
8.6 

8.6 
8.3 
8.3 
8.2 
8.2 
8.2 
8.2 
9.3 


485 
485 
485 

450 

500 
420 
485 
485 
485 
485 
540 


57 


. 67.6 


58 


74.1 


59 


... 76.0 


60 


76.0 


61 . 


76.0 


62 


76 


63 


76.0 


64 


... 76.0 


65 


76 


66 


76 


67 


. . 76.0 


68 


76.0 


69 


76.0 


.45 
.30 
.26 
.74 

.74 


9.1 
8.3 
8.3 
7.7 
7.7 


480 
485 
485 
690 
690 


70 


... 76.0 


71 . . 


73.6 


72 


66 6 


73. . 


. 66.4 


74. . 


... 72.8 


75 


... 74.0 


.83 

1 '.55 
.35 
.50 


7.7 

's'.i 

8.1 
8.1 


690 

385 
455 
410 


76. . 


74.0 


77 


74 


78 ... 


76.2 


79. . 


... 76.2 


80 


... 76.2 


81 .. 


82.6 


L10 


24.8 


500 







These panels were painted without using the shield or cleaning the cup 
after painting each panel. Average values are given for successive 
panels when the same paint was used. 

Inspections 

Inspections were made each year (1950 through 1959, with the 
exception of 1955) by members of the Farm Structures Division of 
the Department of Agricultural Engineering. Since most of the in- 
spectors worked with the project four years in succession, they de- 
veloped proficiency in judging the panels. The yearly inspections were 
made by the inspectors viewing each panel from a platform at eave 
height. A high platform was built over a pickup truck so that it could 
be moved along the eaves as the inspections were made. Each panel 
was studied and the percent of film failure was recorded. The north 
and south exposures were inspected separately. 

Criteria for Evaluating Tests 

An important consideration in evaluating paint tests is to select an 
objective method for determining the life of a paint system. Browne 
(2) lists people in four categories according to their use of paint as 



14 



BULLETIN NO. 676 



[August, 



those who (a) paint for appearance; (b) paint when the film shows 
signs of failing but is not badly deteriorated; (c) paint long after the 
surface should have been painted; and (d) do not paint at all. 

Obviously, each of these groups has a different idea of when the 
"repaint stage" is reached. To evaluate paint tests, the repaint stage 
must be defined. Singleton (9) states that "To the larger body of 
technical men who are paint users rather than paint makers, panel tests 
are only incidental. These men are concerned with the cost and the 
quality of protection that the paint will give on structures in service. 
The goal of panel testing should be not merely to compare different 
paint combinations, but to determine the life of the paint on the struc- 
ture. The results should be a quantitative figure representing the life 
of the paint system in months or years to a stage where repainting is 
necessary." 

One way to define repaint stage is to compare the condition of a 
panel with the ASTM photographic standards (12) as adopted in 1943 
and reapproved without change in 1958. Numerous authorities (Sin- 
gleton, Walton, Burgener) have recommended ASTM No. 8 as the 
stage in the photographic standards when repainting is necessary 
(Fig. 4). This standard corresponds to a film failure of about 5 per- 
cent (4). For comparison of paint performance in this test, 5-percent 
film failure was used as the repaint stage. All panels did not reach 
5-percent film failure or repaint stage during the 10-year test period. 




Photographic reference standard Number 8 type 1, rusting not accompanied by blister- 
ing. This standard has often been recommended as the "repaint stage." Photo courtesy 
American Society for Testing Materials. (See literature citation 12.) (Fig. 4) 



7967] PAINT TESTS ON GALVANIZED ROOFING 15 

TEST RESULTS 

Performance of Paint Systems 

The paint-performance data for all paint systems are summarized 
in Table 3. The average percent film- failure ratings are listed for the 
9 inspections (1949 to 1959, with the exception of 1955). The percent 
film-failure rating is an estimate of the percent of total area of the 
panel where the paint film failed and rust occurred. The southern and 
northern exposures of each panel were graded separately. Since the 
panels had one replication, the film- failure values listed in the table 
are an average for two panels. For the sake of convenience, any film 
failure below 1 percent was coded as 0.5 percent. 

The relative durability of each paint system is shown by the "time 
to repaint stage." This stage represents the approximate time at which 
5 percent of the surface of the test panel was devoid of paint. In the 
two-coat systems, the degree of failure applied to both coats of paint. 
A number of paint systems did not have a film failure of 5 percent at 
the end of 10 years and, therefore, did not reach repaint stage. 

Table 4 lists the 15 paint systems with the smallest percent of film 
failure after 10 years' exposure. Since most of the panels did not 
reach repaint stage in 10 years, the paints were ranked according to 
the average percent film failure at that time. The last four paint sys- 
tems reached the repaint stage before the end of 10 years. 

The aluminum paints used as a second coat over red lead or gray 
MZP (Metallic Zinc Paint) gave the best overall performance. All of 
the panels painted a first coat of red lead and a second coat of one of 
the aluminum paints (other than asphalt aluminum) performed well. 
A large number of the panels painted with a base coat of gray MZP and 
a second coat of one of the aluminum paints did not reach repaint stage 
after 10 years' exposure. The panels with two coats of gray MZP were 
nearing repaint stage at the end of 10 years. 

Table 5 summarizes the results of all one-coat paint systems and 
all paint systems composed of two coats of the same paint. In the one- 
coat paint systems, the performance of red MZP and gray MZP was 
about the same. Each gave approximately 5 years' protection before 
repaint stage. All single-coat paint systems of MZP gave a better 
performance than single coats of aluminum paint. 

When two applications of the same paint were used, gray MZP 
(soybean oil, paint No. 1) gave the best performance over 10 years' 
protection. The paint system composed of two coats of aluminum 
(paint No. 12, aluminum for metal and masonry) protected the panel 
for over 8 years before repaint stage was reached. 



16 



BULLETIN NO. 676 



[August, 



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796?] 



PAINT TESTS ON GALVANIZED ROOFING 



17 



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BULLETIN NO. 676 


[August, 






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796?] 



PAINT TESTS ON GALVANIZED ROOFING 



19 



Table 4. Performance of Paint Systems With Smallest Percent 
of Film Failure 



Rank 


Paint 
system 


Paint 
No." 
(first 
coat) 


Paint 
No." 
(second 
coat) 


Film failure at 10 years, percent 


Southern 
exposure 6 


Northern 
exposure 1 ' 


Average 


1.. 


29 


18 
18 

1 
11 
1 
1 
1 
5 
1 
16 
12 
13 
1 
4 
3 


19 
17 
14 
12 
19 
12 
15 
12 
1 
15 
12 
12 
3 
12 
3 


.25 
.50 
1.75 
2.50 
5.00 
3.50 
4.50 
6.00 
5.00 
2.50 
3.00 
2.50 
13.50 
3.50 
14.00 


2.50 
2.75 
3.00 
2.25 
.50 
2.75 
3.00 
3.00 
4.25 
7.00 
6.50 
10.00 

10.50 
1.00 


1.38 
1.62 
2.38 
2.38 
2.75 
3.12 
3.75 
4.50 
4.62 
4.75 
4.75 
6.25 d 
6.75 d 
7.00 d 
7.50 d 


2 


25 


3 


38 


4 


... 13 


5 


... 30 


6 


20 


7 


21 


8 


16a 


9 


40 


10 


26 


11 


36 


12 


15 


13 


2 


14 


17 


15 


7 







A detailed description of the paints is given in Table 1. 
b Except for Paint System 16a, all values are the average of two panels. 
c Film-failure value is for only one panel. See footnote g, Table 3. 
d Reached repaint stage before the end of 10 years. 



Table 5. Performance of One-Coat Paint Systems and Paint Systems 
With Two Coats of the Same Paint 



Rank 


Paint 
system 


Paint 
No." 


Film failure at 10 years, 


percent 


Time to 
repaint 
stage 
(years) 


Southern 
exposure 6 


Northern 
exposure 6 


Average 


1.. 


8 


One-coat paint 
3 38.5 
1 15.0 
9 48.5 
14 90.0 
12 47.5 
17 87.5 
20 87.5 

Two-coat paint 
1 5.0 
12 3.0 
3 14.0 
17 5.0 
9 17. O d 
20 24.5 
14 21.0 
8 47.5 
22 57.5 


systems 
13.00 
29.00 
25.00 
70.00 
53.50 
80.00 
92.50 

systems 
4.25 
6.50 
1.00 
11.00 
5.00 d 
44.00 
19.00 
46.00 
52.00 


28.50 
22.00 
36.80 
80.00 
50.50 
83.80 
90.00 

4.62 
4.75 
7.50 
8.00 
11.00 
34.25 
20.00 
46.50 
54.75 


sy 2 

5 
3 
1 

1 A 
1 A 

y 2 

over 10 
over S^2 
over 8 

lYi 
7H 
4', 

4 
4 
2 


2 


39 


3 


10 


4 


18 


5 


35 


6 


... 27 


7 


33 


1.. 


40 


2 


36 


3 


7 


4 


28 


5 


lib 


6.. 


32 


7 


19 


8 


9 


9 


37 







A detailed description of the paints is given in Table 1. 

b Except for Paint System lib, all values are the average of two panels. 

c Values were calculated to the nearest one-half year. 

d Film-failure value is for only one panel. See footnote f, Table 3. 



20 



BULLETIN NO. 676 



[August, 



Table 6 summarizes the results of all paint systems that had a base 
coat of gray MZP. In general, the paint systems that had an alumi- 
num paint top coat over a gray MZP base coat again gave the best 
performances. 

Table 6. Performance of Paint Systems With Gray MZP Base Coat 



Rank 


Paint 
system 


Paint 
No. a 
(first 
coat) 


Paint 
No. a 
(second 
coat) 


Film failure at 10 years, percent 


Time to 
repaint 
stage 
(years) 


Southern 
exposure 11 


Northern 
exposure 11 


Average 


1 


38 


1 
11 
1 
1 
1 
1 
16 
1 
1 
16 
11 
1 
1 


14 
12 
12 
15 
19 
1 
15 
3 
17 
17 
17 
20 
2 


1.75 
2.50 
3.50 
4.50 
5.00 
5.00 
2.50 
13.50 
9.50 
17.50 
13.00 
12.50 
17.00 


3.00 

2.25 
2.75 
3.00 
.50 
4.25 
7.00 

7.50 
7.75 
8.50 
9.00 
11.00 


2.37 
2.37 
3.12 
3.75 
2.75 
4.62 
4.70 
6.75 
8.50 
12.62 
10.75 
10.75 
14.00 


over 10 
over 10 
over 10 
over 10 
over 10 
over 10 
over 9 
over 8 
7 
6H 
6H 
6 
4^ 


2 


. . 13 


3 


20 


4.. 


. . . 21 


5 


... 30 


6 


.. . 40 


7 


. .. 26 


8 . . . 


2 


9 


. 22 


10 


24 


11 


. .. 23 


12 


.. . 31 


13 


1 







A detailed description of the paints is given in Table 1. 

b All values are the average of two panels. 

c Values were calculated to the nearest one-half year. 



Figs. 5 through 8 show the performance over the 10-year period 
of the metallic zinc paints, the aluminum paints, all paint systems with 
a gray MZP base coat, and all paint systems with red lead, white lead, 
or zinc chromate for the base coat, respectively. All values on these 
graphs are averages for north and south exposures. 

Effect of Exposure 

Exposure had an appreciable effect on the performance of the red 
and green paints, but no apparent effect on the paint systems with an 
aluminum paint top coat. Table 7 summarizes the 10-year performance 
of all paint systems with a red or green top coat and all paints with 
an aluminum paint top coat. 

In every case, the film failures from the paint systems with a red 
or green top coat were larger for the southern exposure than for the 
northern exposure. The exposure did not seem to affect the perform- 
ance of the paint systems that had a second coat of one of the aluminum 
paints. Fig. 9 shows the contrast between the two groups of paints. 
The average film failures at 10 years were almost equal (20.3 compared 
with 22.0) for the northern and southern exposures of the paint systems 



J96J] PAINT TESTS ON GALVANIZED ROOFING 21 

Table 7. Effect of Southern and Northern Exposures 
on Paint Performance 



Film failure at 


Paint 


Paint No." 


Paint No. 


10 years, 


percent 


system 


(first coat) 


(second coat) 


Southern 


Northern 








exposure 6 


exposure 6 


Paint systems with red and green 


top coats 




2 


1 


3 


13.50 





3 


4 


3 


23.50 


.25 


4 


5 


3 


55.00 


7.50 


5 


6 


3 


53.50 


9.00 


6 


7 


3 


25.00 


3.00 


7 


3 


3 


14.00 


1.00 


8 


3 


none 


38.50 


13.00 


10 


9 


none 


48.50 


25.00 


lla 


9 


10 


55.00" 


1.00 


lib 


9 


9 


17. 00 


5.00 


12 


10 


9 


22.50 


8.75 


Average. ... 






34.50 


9.90 


Paint systems with aluminum top 


coats 




13 


11 


12 


2.50 


2.25 


14 


6 


12 


3.50 


17.00 


15 


13 


12 


2.50 


10.00 


16a 


5 


12 


6.00" 


3.00' 


16b 


23 


12 


4.00" 


65.00 C 


17 


4 


12 


3.00 


10.50 


18 


14 


none 


90.00 


70.50 


19 ... 


14 


14 


21.00 


19.50 


20 


1 


12 


3.50 


2.75 


21 


1 


15 


4.50 


3.00 


22 


1 


17 


9.50 


7.50 


23 


11 


17 


13.00 


8.50 


24 


16 


17 


17.50 


7.75 


25 


18 


17 


.25 


.50 


26 


16 


15 


2.50 


7.00 


27 


17 


none 


87.50 


80.00 


28 


17 


17 


5.00 


11 50 


29 


18 


19 


.25 


2.50 


30 


1 


19 


5.00 


.50 


31 


1 


20 


12.50 


9.00 


32 


20 


20 


24.50 


44.00 


33 


20 


none 


87.50 


92.50 


34 


21 


20 


33.50 


5.50 


35 


12 


none 


47.50 


53.50 


36 


12 


12 


3.00 


6.50 


37 


22 


22 


57.50 


52.50 


38 


1 


14 


1.75 


3.00 


Average. ... 






20.30 


22.00 



* A detailed description of the paints is given in Table 1. 

b Except for Paint Systems lla, lib, 16a, and 16b, all values are the average of two panels. 

c Film-failure values are for only one panel. See footnotes f and g, Table 3. 



22 



BULLETIN NO. 676 



[August, 



that had an aluminum second coat. There was a large difference, how- 
ever (34.5 compared with 9.9), between paint systems with a second 
coat of red or green paint. The kind of exposure did not seem to affect 
the performance of the gray MZP. 

Effect of Original Condition of Sheet 

The original condition of the metal sheets on the test crib varied 
from 45 to 100 percent rusty (see Table 3). 

The panels on the northern exposure for the second replication 
were 100 percent rusty when they were painted, and the average film 
failure at the end of 10 years was 28.4 percent. The panels for the 
first replication on the northern exposure varied from 50 to 90 percent 
rusty, with an average of 65 percent rusty, and the average film failure 



PAINT SYSTEMS 



(TWO COATS) 

(TWO COATS) o 

(TWO COATS) o 

(ONE COAT) 

(ONE COAT) 

(ONE COAT) 



40 - GRAY MZP 

7 - RED MZP 
lib - GREEN MZP 
39 - GRAY MZP 

8 - RED MZP 
10 - GREEN MZP 




234567 

EXPOSURE TIME IN YEARS 

Performance of metallic zinc paints. 



(Fig. 5) 



?96I] 



PAINT TESTS ON GALVANIZED ROOFING 



23 



PAINT SYSTEMS 

36 - AL.FOR METAL t MASONRY(I) (TWO COATS) 
28 - AL (RUST- RESISTING VEHICLE) (TWO COATS) 

34 - ASBESTOS ASPHALT (111 COAT) 

ASPHALT AL (2<tf COAT) 

19 - AL. GENERAL PURPOSE (I) (TWO COATS) 

32 - ASPHALT ALUMINUM (TWO COATS) 

35 - AL.FOR METAL t MASONRY (I) (ONE COAT) 
37- AL, SPECIAL (TWO COATS) 
18- AL. GENERAL PURPOSE (I) (ONE COAT) 
27 - AL (RUST-RESISTING VEHICLEKONE COAT) 

33 - ASPHALT ALUMINUM (ONE COAT) 



23456 
EXPOSURE TIME IN YEARS 



7 8 9 10 




Performance of aluminum paints. 



at the end of 10 years was only 7.8 percent. The difference between 
these two averages indicates that the original condition of the panels 
had a definite effect on the performance of the paint systems. 

Effect of Wire Brushing Sheets Before Applying Paint 

One of the objectives of this test was to evaluate the practice of 
brushing a rusty galvanized sheet before applying paint. In prepara- 
tion for painting, all of the panels were swept with a broom to remove 
all foreign material. 

The top portions of the bottom sheets of panels 46 through 81 on 
the northern exposure were wire brushed before painting (Fig. 10). 
These sheets were inspected each year. During the tenth yearly in- 



24 



BULLETIN NO. 676 



[Aogojf, 



spection, panels 46 through 81 were studied with special care to see 
if any difference existed between the paint performance of the sections 
that had been wire brushed and the remaining portions of the panels. 
As far as could be determined, the wire brushing had no effect on the 
ability of the paint to withstand weathering. 

This conclusion agrees with the rinding of Walton (13). After a 
7-year paint study at Pennsylvania State University, Walton stated 
that "In preparing a rusty steel roof for painting, it is unnecessary to 
wire brush the surface to free it of rusty particles. It will be sufficient 
to whisk the surface free of loose particles of foreign matter." 
Matthews (8) also observed that steel brushing was unnecessary in 
the preparation of rusty galvanized sheets for painting. 



PAINT SYSTEMS 

SECOND COAT 



1 3 - GRAY 
38 -GRAY 
30 -GRAY 
20- GRAY 

2 I - GRAY 
40 -GRAY 
26 -GRAY 

2 -GRAY 
22 -GRAY 

3 I - GRAY 
23- GRAY 
24 GRAY 

I - GRAY 
39 - GRAY 



MZP (LINSEED OIL) 
MZP (SOYBEAN OIL) 
MZP (SOYBEAN OIL) 
MZP (SOYBEAN OIL) 
MZP (SOYBEAN OIL) 
MZP (SOYBEAN OIL) 
MZP PRIMER 
MZP (SOYBEAN OIL) 
MZP (SOYBEAN OIL) 
MZP (SOYBEAN OIL) 
MZP (LINSEED OIL) 
MZP PRIMER 
MZP (SOYBEAN OIL) 
MZP (SOYBEAN OK.) 



AL, FOR METAL C MASONRY (I) 

AL, GENERAL PURPOSE (I) 

AL, TOR METAL $ MASONRY IE) 

AL, FOR METAL 6 MASONRY (I) 

AL, GENERAL PURPOSE (D) 

GRAY MZP (SOYBEAN OIL) 

AL, GENERAL PURPOSE (H) 

RED MZP 

AL (RUST- RESISTING VEHICLE) 

ASPHALT ALUMINUM 

AL (RUST- RESISTING VEHICLE) 

AL (RUST- RESISTING VEHICLE) 

GRAPHITE 

NONE 




3456 
EXPOSURE TIME IN YEARS 



Performance of paint systems with gray MZP for a first coat. 



(Fig. 7) 



J967] 



PAINT TESTS ON GALVANIZED ROOFING 



25 



SYSTEMS 

SECOND COAT 



29-RED LEAD OXIDE (LINSEED OIL) 
35 -RED LEAD OXIDE (LINSEED OIL) 
160-ZNC CHROMATE-IRON OXIDE 
15-RED LEAD (SEMI-OUICK-DRYING 

VEHICLE) 

17- ZINC CHROMATE PRIMER 
14- RED LEAD (LINSEED OIL) 

3- ZINC CHROMATE PRIMER 
6- WHITE LEAD 

5- RED LEAD (LINSEED OIL) 

4- ZINC CHROMATE-IRON OXDE 



AL, FOR METAL 4 MASONRY (H) 
AL (RUST-RESISTING VEHICLE) 
AL, FOR METAL t MASONRY (I) -- 
AL, FOR METAL t MASONRY (I) 



AL. FOR METAL t MASONRY (I) 
AL, FOR METAL $ MASONRY (I) 
RED MZP - 

RED MZP 

RED MZP 




EXPOSURE TIME IN YEARS 

Performance of paint systems with red lead, white lead, or zinc chromate for a first coat. 

(Fig. 8) 



RED AND GREEN TOP COATS 



ALUMINUM TOP COATS 



5 10 15 20 25 30 35 

AVERAGE PERCENT OF FILM FAILURE AT THE END OF 10 YEARS 

Effect of exposure on red and green top coats and aluminum top coats (Fig. 9) 



26 



BULLETIN NO. 676 



[August, 




The top portions of the bottom sheets of Panels 46 through 81 on the north side were 
wire brushed before painting. These panels were 100 percent rusty (see Fig. 2). (Fig. 10) 



SUMMARY 

Among the general conclusions drawn from this study, the follow- 
ing are most significant. 

1. Exposure had a definite effect on the paint systems with a red 
or green top coat, but no apparent effect on the paint systems with an 
aluminum top coat. All panels with a paint system composed of a red 
or green top coat had an appreciably larger film failure on the southern 
exposure than on the northern exposure. There was no significant 
difference between film failures on the northern and southern ex- 
posures for the aluminum top coats, or for the gray MZP top coat. 

2. The original condition of the panel affected the amount of pro- 
tection offered by the paint system. The greater the amount of rust 
when the panel was painted, the faster the paint film failed. 

3. The paint systems that provided the best protection were those 
with a first coat of red lead and a second coat of an aluminum paint 
and those with a first coat of gray metallic zinc paint and a second 
coat of an aluminum paint. 

4. Wire brushing before painting gave no apparent increased pro- 
tection to the panels. If the panels had not been brushed, however, 
more paint would have been necessary to secure a good coverage. 



J96J] PAINT TESTS ON GALVANIZED ROOFING 27 

LITERATURE CITATIONS 

1. BARTELLS, G. C. Test results of metallic zinc paint on galvanized sheet metal. 

Agr. Engin. 20:101-103. 1939. 

2. BROWNE, F. L. Testing house paints for durability. U. S. Dept. Agr. Forest 

Prod. Lab., Madison, Wis. 

3. BURGENER, M. L., and CARTER, D. G. Protective coatings for weathered gal- 

vanized sheets. Agr. Engin. 31:67-70. 1950. 

4. BURGENER, M. L., and CARTER, D. G. Durability of paints on weathered gal- 

vanized roofing. 111. Agr. Exp. Sta. Bui. 565. 16p. 1953. 

5. EVANS, U. R. Metallic corrosion passivity and protection. Edward Arnold 

and Co. London. 720p. 1938. 

6. HOCKER, C. D. Outdoor test results on bare and metal-coated ferrous speci- 

mens. Symposium on the outdoor weathering of metals and metallic 
coatings, pp. 1-19. Regional meeting ASTM, Washington, D. C. 1934. 

7. IRISH, W. W. Illinois farm building activities and trends, 1944-1954. Un- 

published Master's thesis. Univ. of 111. 1955. 

8. MATTHEWS, C. A. Spray painting farm metal roofs. Agr. Engin. 29:542-544. 

1948. 

9. SINGLETON, W. F. The interpretation of visual rusting standards. Proc. 

ASTM 44:910-915. 1944. 

10. SPELLER, F. N. Corrosion, causes and prevention. McGraw-Hill. New York. 

686p. 3d ed. 1951. 

11. Standard method of conducting exterior exposure tests of paint on steel 

(D1014-51). ASTM Standards 8:846-874. 1958. 

12. Standard method of evaluating degree of resistance to rusting obtained with 

paint on iron and steel surfaces (D610-43). ASTM Standards 8:875-880. 
1958. 

13. WALTON, H. V. Painting galvanized steel roofing: exposure studies. Pa. 

Agr. Exp. Sta. Prog. Rpt. 139. lip. 1955. 



6M 8-61 74507 



UNIVERSITY OF ILLINOIS- URBAWA 

Q.630.7IL6B C008 

BULLETIN URBANA 
6761961 




30112019530408