water content vs
Water Absorption by Polyether Flashing

These 7-day water absorption curves compare ten polyether liquid flashings. I use these data to make several points.

Water absorption varies within this diverse class of products. And I’m finding its correlation with adhesion, especially with certain substrates. Our industry doesn’t give all of this much thought; which is rather odd considering that adhesion of these same products are often tested after 7-day immersion per AAMA 714.  Of course those methods consider anodized aluminum as the test substrate, not the substrates to which these products are typically applied. But it gets worse.  When evaluating water absorption, we rely too heavily on 24-hour immersion per ASTM D570.  And magically all products pass a commonly reported 1% threshold. I smell a rat (another topic).

When we conjoin findings from different test methods, expecting clarity in predicted performance, we can get a false impression of the product’s actual attributes. In other words, adhesion characteristics derived from 7-day immersion tests on aluminum tell us very little about post-immersion adhesion on glass mat facers. Now add an AWB, and our results are even different. And that a liquid flashing absorbs less than 1% water after 24 hours tells us nothing about absorption at seven days and beyond.

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M. Steven Dogget, Ph. D.

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