Membrane Roof Blisters: How to Prevent & Repair Them Effectively

Blistering is a common issue on commercial roofing membranes that can range from cosmetic to serious. Here's what building owners need to know.

What Causes Roof Blisters

Blisters form when air or moisture becomes trapped beneath or within the membrane during installation. Heat from the sun causes trapped gas or moisture to expand, creating a dome-shaped bubble. Common causes: damp substrate at installation, solvent evaporation from adhesives, inadequate bonding during heat welding, and moisture infiltration through breaches that becomes trapped.

Types of Blisters

Interply blisters (between plies of BUR): typically less serious, may be monitored. Membrane-to-substrate blisters: more serious, indicate adhesion failure. Foam blisters (on spray foam systems): most serious — indicate wet insulation beneath the foam.

When Blisters Are Serious

Small, stable blisters that aren't growing may be monitored. Blisters that are large, growing, or rupturing require immediate attention. Ruptured blisters create active leak pathways. Any blister on a spray foam roof indicates wet insulation beneath — investigate immediately.

Repair Approaches

Small, intact blisters: may be left alone with monitoring. Large blisters: cut, allow to dry, fill with compatible material, patch and seal. Widespread blistering: indicates system-level issues requiring comprehensive restoration assessment. Blistered foam sections: remove blistered foam, address wet insulation, re-foam and recoat.