TIL the hard way that moisture readings on concrete can be misleading

I had a job in Portland last year where the slab passed a calcium chloride test but failed the RH probe test two days later. The homeowner wanted to save money so we pushed ahead anyway, and now the glue-down vinyl plank is starting to bubble near the seams. Has anyone else had the experience of one test passing and the other failing, and which one do you usually trust?

2 comments

2 Comments

mila3956d ago

Yeah I read somewhere that RH tests are more accurate for concrete because they actually measure the moisture deep inside the slab. Calcium chloride only catches surface stuff.

keith9436d ago

Oh man, that's close but not exactly right. RH tests actually measure the moisture in the pores of the concrete, which is deeper than what calcium chloride tests catch, sure. But the thing is, RH tests aren't necessarily more accurate overall. They give different info. Calcium chloride measures how much moisture is actually leaving the slab, which is what matters for most floor coverings. RH tests can give you readings that are technically high but the surface might be fine to work with, especially if the slab has been curing properly. So you gotta know what you're looking for.