Tech
Blisters, bubbles and bond loss: tracking down moisture problems
The warning signs, the tests that matter and when you need a moisture vapor barrier.
By Tech rep team · Jun 25, 2026 · 9 min read
Moisture-related failures usually show up weeks or months after install as blisters, hollow spots or coatings peeling in sheets. Almost all of them are preventable with testing up front.
Test before you coat
Calcium chloride (ASTM F1869) and in-situ RH probes (ASTM F2170) tell you how much vapor the slab is emitting. Slabs on grade without a vapor retarder are the usual suspects.
When to use an MVB
If RH tests above your coating's limit — often 75–85% for standard epoxy — install a moisture vapor barrier epoxy rated for the measured level before your build coat.
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