Brittle testing and pliability testing of asphalt shingles are two terms often misused in asphalt shingle rejuvenation. Although frequently used interchangeably, they refer to different methodologies to test the flexibility of a shingle.
What is Brittle Testing?
A brittle test is a roofing inspection method to evaluate shingle pliability and repairability. This test involves unbinding a field shingle from the shingle below it, lifting it 45 degrees three times, and checking for any cracks or breakage. Often touted incorrectly as an ASTM test, the field-performed brittle test is invalid due to the lack of specificity, procedure, and consistency. Inspectors use different lifting forces, lift dimensions, lift angles, and failure criteria, which can cause shingle damage regardless of age or condition.
Furthermore, the lack of an accepted methodology makes it impossible to carry out the brittle test in a repeatable scientific way. And the anecdotal nature of the brittle test makes it likely to cause shingle damage upon its performance, even on brand-new roofs.
ASTM Pliability Testing an Asphalt Shingle
On the other hand, the ASTM D3462 Pliability Test is a more reliable method for measuring shingle flexibility. By including uniform test controls and accounting for bend radius and temperature, ASTM D3462 yields reliable, repeatable results when testing the flexibility of asphalt shingles.
The ASTM D3462 Pliability Test involves bending a shingle over a cylindrical mandrel, a curved object of a defined radius, and then inspecting the shingle for cracks, rips, and tears. Below is an example of ASTM D3462.
Digging Deeper Into the Brittle Test
The folks over at HAAG Engineering have an excellent post on the brittle test and why the results are invalid here. But in short, the brittle test is unscientific and does not yield repeatable results. At the same time, ASTM D3462 accounts for variables that alter the properties of shingles, such as temperature and bend radius. It will yield accurate and repeatable results when trying to determine if an asphalt shingle needs replacement.
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