TIL that skipping moisture tests on concrete slabs before laying adhesive... nearly cost me a full reinstall on a commercial job.

3 comments

3 Comments

But how do you decide which slabs get a pass on testing and which ones don't? If a visual check looks good but the concrete is secretly holding moisture, the adhesive failure might not show up for months, long after everyone's been paid. Isn't trusting the data sheets exactly why they list a maximum moisture level for the adhesive to work? Seems like gambling the whole install on a dry-looking surface could cost way more than a two-day delay.

jamie_johnson8d ago

Try the plastic sheet test overnight, it tells you plenty.

barnes.skyler9d ago

Honestly, this idea that skipping a moisture test "nearly cost" you feels like fear-based thinking. On tight-deadline commercial jobs, waiting 48 hours for test results can blow the schedule, and I've seen plenty of slabs that passed a visual inspection (no dark spots, no efflorescence) hold adhesive just fine for years. Modern adhesives are way more forgiving than the old stuff, and sometimes you have to trust the product data sheets and just get the floor down. A blanket rule for testing every single slab ignores the reality of project timelines and budget constraints.