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?

3 comments

3 Comments

pat_moore27d 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_anthony27d ago

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

jesse_price2726d 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.