My moisture meter read 22% in a basement I was sure was dry

I was prepping for a glue down LVT job in this old house basement last month, figured it was fine since it felt dry and the homeowner said it never floods. Pulled out my Wagner MMC220 just to be safe, and the number jumped to 22% right in the center of the slab. That's way over the 4% max for most adhesives. It mattered because I was about to lay about 800 square feet of material that would have failed in a year. Turns out there was a slow leak from a buried downspout outside. Had to delay the job a full week for a French drain install and drying time. Saved my butt and the client's floor. What's the highest reading you've ever gotten that made you stop a job in its tracks?

2 comments

2 Comments

the_sandra23d ago

Found 45% once, slab was basically a sponge.

joseph_murray823d ago

Forty five percent is a big number, but I have to wonder about the test method. Was that a core sample from the middle of the slab or a surface reading? Surface moisture can be way off. I've seen meters go wild over a bit of leftover curing compound. Unless they drilled down for a real check, it might just be a damp spot, not a structural issue. A truly soaked slab would have way more obvious problems, like major cracking or efflorescence.