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no. 676 cop. 8

UNIVERSITY OF

ILLINOIS LIBRARY

AT URBANA-CHAMPAIGN

AGRICULTURE

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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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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

14b

... 76.0

15

... 76.0

16b

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 0

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 0

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 0

45b

... 76.0

46>>...

76.0

47

... 76.0

48

76 0

49b

... 76.0

50 . .

76 0

2.60

13.5

395

51. .

76 0

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 0

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 0

63

76.0

64

... 76.0

65

76 0

66

76 0

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 0

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

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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 exposure6

Northern exposure1'

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 0 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 6.25d 6.75d 7.00d 7.50d

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)0

Southern exposure6

Northern exposure6

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. Od 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 5.00d 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

sy2

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4 4 2

2

39

3

10

4

18

5

35

6

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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)0

Southern exposure11

Northern exposure11

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 0 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

exposure6

exposure6

Paint systems with red and green

top coats

2

1

3

13.50

0

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"

65.00C

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

0 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

0 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

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