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Update: I saw a huge difference in plank cupping after switching from a 6-mil to a 10-mil vapor barrier on a slab job.
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the_michael5mo ago
My buddy had the same problem with a garage floor. He used a thin barrier and the tiles looked awful after one winter. @james92 mentioning tar paper made me think of it, that old stuff fails the same way. The thicker 10-mil stuff just moves less with the slab. It's a cheap fix now that saves a huge headache later. He had to tear everything out and start over.
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sam_anderson3mo ago
Nodding along with @the_michael on this one. The thickness really does make or break it because thin barriers can't handle the slab moving under temperature changes. My neighbor went with 6-mil plastic sheeting and within a year you could see every crack and uneven spot through his tiles. He had to rip it all out and start fresh with 10-mil and a proper underlayment. It's one of those things where spending an extra $40 on material saves you from a $400 redo later. Have you tried looking at the fiberglass reinforced ones, or do you prefer the straight plastic sheeting?
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james925mo ago
We had a similar issue with a basement floor in a 1950s house. The original builder used tar paper as a barrier, and you could see every single crack telegraphing through the vinyl tile they put down later. It was a real mess to fix.
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