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My uncle told me to never use a moisture barrier on a slab with radiant heat | Flooring Installers - Free To Speak

My uncle told me to never use a moisture barrier on a slab with radiant heat

Honestly, my uncle Frank, who's been laying floors since the 80s, swore up and down that putting a moisture barrier over a heated slab would trap vapor and cause the adhesive to fail. I did a job in a new build in Springfield last month with in-floor heat, and I almost skipped the barrier because of him. Ngl, I'm glad I didn't. I tested the slab with my Tramex meter anyway and it was reading 85% RH. I put down the barrier, followed the adhesive specs to the letter, and checked back after a week. The floor is perfect, no bubbles, no lifting. If I'd listened to him, I'd be ripping up 800 square feet of LVP right now. Has anyone else had an old-timer give them advice that just doesn't hold up with modern materials?

4 comments

4 Comments

pat_moore6mo ago

My uncle Frank sounds like a guy who learned on the job, and those guys are usually right until they aren't. But I gotta ask, how many times has this actually been a problem? You had a wet slab, so you used a barrier. That's just following the meter. But on a properly cured slab that tests dry, is skipping it really that big of a deal? I've seen plenty of installs over radiant without a barrier that are fine years later. Sometimes I wonder if we're solving problems that aren't really there with all these extra steps.

the_anthony6mo ago

Nah, it's gambling with someone else's house. Seen too many callbacks for moisture issues that could've been avoided.

aaron7405mo ago

My shop's warranty claims dropped by half after we started testing every slab.

jesse_price276mo ago

Wait, your meter said 85% RH on a new build? That's a seriously wet slab! Frank's rule might work on old, bone-dry concrete, but that's a whole different story. Skipping the barrier there would have been a total disaster.