Volume 16, Issue 3 (May 1988)
Granule Embedment on Shingles and Roofing Membranes
Samples of shingles and modified bituminous membranes covered with stone, slag or slate granules were tested for the amount of granules applied and the coverage provided to the bitumen. The granule embedment in the as-received condition and after wetting was measured by scrubbing the samples with 50 strokes of a steel wire brush. Five representative samples out of the thirteen were also subjected to an extended scrub test, where the number of scrub strokes was increased to 150 (in intervals) to evaluate the retention. The results showed significant variations between samples.
The requirement of a fixed amount of granule loss exists in most standards. Although this is adequate for quality control, the loss should be proportional to the quantity of granules applied, rather than a fixed amount. Proper assessment of granule adhesion requires testing for wet granule loss, for the initial granule coverage and for the tendency for granules to detach under extended scrubbing.