I finally stopped using a 6 mil vapor barrier on every slab job after a guy in Phoenix called me out

For years I just slapped down that thin plastic under everything, thinking it was the standard move. Then on a big condo project last fall, this older installer from Arizona saw me rolling it out and said, 'Kid, you're just making a mold sandwich with that stuff in our climate.' He explained that in a lot of dry areas, or on slabs that already have a proper moisture barrier below, that extra plastic can trap any tiny bit of moisture that does come up against the concrete, and it has nowhere to go but into your flooring. I switched to using a thicker, breathable underlayment with a perm rating for most jobs now, unless the specs or a moisture test really call for the plastic. It was a simple change but it made me actually think about what the barrier is supposed to do, not just follow old habits. Has anyone else had a similar wake-up call about vapor barriers?

2 comments

2 Comments

the_susan17d ago

Man, that's such a good point. I got stuck in the same routine for way too long.

nguyen.dylan17d ago

Yeah, my buddy got stuck like that too, @the_susan.