How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What causes bubble-like blisters in a built-up and gravel roof?
Saturday, June 16, 2018
When moisture seeps between the plies of a built-up and gravel roof, and then the sun comes out and heats up the surface, the water turns to vapor. Expansion of the trapped gas causes a raised pocket, known as a blister, to form. The blister will often loosen the gravel and some of it will slide away from the area, allowing more deterioration, and leakage.
An older blister like the one shown in the photo at the top of this page is not just visible. When you step on it, the blister makes a squishy sound from the trapped water inside.
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