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I used to think a 6 mil vapor barrier was enough for any slab, but a job in Seattle changed that.
I was doing a glue-down LVT install in a basement over a concrete slab. The homeowner said they had a 6 mil poly down, so I figured we were good. Two days after we finished, the floor started to cup along the edges. Turns out, the slab was still putting out a lot of moisture, even with that barrier. A local supplier told me that in high-humidity areas, you really need to test the slab and sometimes use a 10 mil or even a thicker, taped system. Now I always do a calcium chloride test before I even quote a job on a slab. Has anyone else run into this with older homes near the water?
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