TECHNICAL INFORMATION ON BUILDING MATERIALS

TIBM - 51

FOR USE IN THE DESIGN OF LOW-COST HOUSING

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THE NATIONAL BUREAU OF STANDARDS

UNITED STATES. DEPARTMENT OF COMMERCE

WASHINGTON, D. C.

September 10, 1937

SHINGLES: MINERAL- SURFACED ASPHALT

This is a brief digest of Research Paper RP1002 , "Accelerated

Weathering Tests of Mineral-Surfaced Asphalt Shingles" (June 1937)

by H. R. Snoke and B. E. Gallup, issued by the National Bureau of

Standards

.

This research -paper covers a detailed investigation of mineralsurfaced asphalt tyre shingles, a comparatively recent development of

the roofing industry, having come into general use within the past

twenty-five years, and particularly adapted to low-cost housing projects, Federal specifications have been adopted for these shingles and

the specification requirements were followed as a basis in this investigation — notably in the analyses of the weight of the various constituents and the total weight per unit area of the finished uroduct.^

Accelerated weathering tests were resorted to because of rauidly

changing conditions in the industry. Outdoor weathering tests would

be out of date before completion, and, hence of no practical value.

Briefly, the accelerated weathering test subjects the samples to con- tinuous light and heat from a carbon-arc lamp (simulating outdoor ex- posure) with intermittent water spray.. Petrographic methods were used

to determine the nature of the granules and of the fine mineral fillers,

although it was found that failures were largely independent of the

granular surfacing material.

Analyses of the thirty-nine samples showed no differences in covroc- sition sufficiently great to warrant the prediction of decided difference

^Maybe obtained from Superintendent of Documents, Washington, D. C.

(Price 10 cents)

p Federal Specification SS-R-521 "Roofing and Shingles: Asphalt, Pre-oared,

Mineral- Surfaced" may be obtained from Superintendent of Documents,

Washington, D. C. (Price 5 cents)

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in their behavior to weathering, exceet that the samples containing fine

mineral filler in the asphalt coatings aunear to be the most resistant

to weathering.

A previous reuort^ found no significant difference in the resistance to outdoor weathering of asuhalt-nrepared roofing that could be

attributed to the kind of fiber or combination of fibers used.

In general, noncompliance with the requirements of the federal

specifications was not evidenced in the results of these tests, although the samples in Group H failed to meet the test of pliability

at 25°C. All roofings developed certain types of failure but retained

commendable features peculiar to their particular brand. A brief description of common failures follows:

COLOR CHANGES : The samples surfaced with oil or resin-coated

granules were the first to show color changes. The alterations were

either a slight fading (for natural slate granules), or an apparent

color intensification (notably the ceramic red granules). In all cases

the natural slate granules- showed the most color changes.

BLISTER : Probably caused by moisture in the' sheet. Accelerated

blister tests and accelerated weathering tests both uroduced blisters,

although of different types.. The former were higher in relation to the

diameter at the base while the latter were relatively low and covered

a larger area. In many cases several small blisters ran together forming a series of connecting blisters.

PITTING : This is closely related to blistering by a further development in which the thin layer of asphalt surrounding the void is

broken. Samples in Groups C and E showed virtually no nits, while those

in the other Groups had more and larger pits arranged as follows in increasing order of severity: B, A, E, .G, D, and H.

LOSS OF GRANULES : 'Tie loss of granules by weight, on weathering,

is greater for the natural slate granules than for the artificial granules.

The loss is less apparent for the natural slate granules because of their

flat shape and scalelike overlapping. The artificial granules, in most

cases, are practically equi dimensional and consequently do not overlap.

Results indicated that initial adhesion of granules, as determined by

abrasion methods, is mainly a function of the. type -of granule rather than

of the asuhalt coating or of the method of manufacture. Abrasion methods

can not be used to predict how well they will adhere on exposure.

H A Study of the 'Weathering Quality of. Roofing Felts Made from Various

Fibers" by 0. G. Strieter, RPSSS; procurable from the Superintendent

of Documents, Government Printing Office, Washington, D. C.

Price 5 cents

2
CRACPIUG : This .defect, urobably one of the most serious, occurred

in relatively few samples.

UAPPPTG ; Samples 3 ^ to 39 * inclusive, (Groups G and H) were distorted the most. Samples 25 to 30 (Group I!

1 ) showed only slight distortion.

All other samples remained practically flat.

SLIPPAGE : The only slippage occurred in the samples in Group C--

auproximately l/U inch at the end of the test.

'The greatest factor in determining the weathering "behavior of these

shingles is due to the tyoes of asrhalt used and the manufacturing

process, excluding large variations in the proportions "by weight of the

several constituents in the finished roofing.

A descriution of the thirty-nine samples of this tyee of roofing

is given in condensed form in the. accompanying table. Under such items

as the weight of the felt and the weight of the surfacing material, it

will "be noted a remarkable uniformity existed between the different

groups.

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