Moisture in slab problem


Old 11-12-09, 12:32 PM
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Moisture in slab problem

Hi everyone, I've got a question which I've posed to multiple people and no one can answer. I've seen similar posts on the forums but am still completely confused.

"Short" backstory: I had a flooring company put down new Bamboo flooring. It was glued down with I believe it's Bostik's Best Adhesive (not water based) and this glue apparently has a moisture barrier in it. Two months later it began cupping/warping and kept getting worse up until it was finally removed. The flooring company did a moisture reading and said we were "in the red" with humidity in the slab at between 22%-100%. (I don't believe they originally took a moisture reading). I've had a 3rd party company confirm the moisture problem.

I've had a foundation specialist and a plumber out as well as discussed with a contractor and two other contractors over the phone. No problems with the plumbing or foundation, no cracks, nothing at all. We don't have any standing water outside our foundation either.

I don't know what else could put the moisture in the slab up so high?! Any thoughts? The flooring company says they've never seen anything like this before. We're trying to lay new engineered flooring down but obviously the flooring company won't do anything until the slab dries out. So as with all renovations we're living in a construction zone until we figure something out but at the same time I don't want to rush into something only to have the same problem happen in a couple months.

I'm stuck now at what to do next but I'm thinking we try to maybe seal the floors? But with what? Home Depot suggested Bostik MVP + Bostik's Best Adhesive and not to float the floors. Lowes suggested some other moisture barrier and to float the floors. The flooring company is suggesting sealing with some sort of Mohawk sealant. Not sure whether floating the floors would make a difference or not with a plastic barrier and a sealer on the concrete under that?!

Sorry so long but does anyone have any thoughts? I'd like to trust the flooring company but it doesn't sound like they've been through this sort of thing before either so I'd really just like to cover all my bases.
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Old 11-12-09, 03:43 PM
Join Date: Oct 2008
Location: New England
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Hi Wed and welcome to the board. You are confirming my position on basements, they can be tough. I'll attach a couple of links that may help, but I also attended a seminar on basements recently that may have something to offer. In the North East we deal with Radon, not sure if Tx has it, but doesn't matter. They corrective measure for Radon has the additional benefit of removing excess moisture from the floor.

First, if your water table is just below the floor or if there is no gravel or plastic vapor barrier with perimeter drainage, then this may not work. But, with a slab over a gravel base, air can be drawn from under the slab and vented to the outside. Our purpose is to depressurize underneath the slab to force any Radon gas to flow to the venting system and thus be removed. With a moisture problem, they stated that moisture levels were reduced as well.

Here is a link for Radon with pictures:

Here are some links for basement issues:

I can't say all of this works, but it is good reading

Old 11-13-09, 07:47 AM
Join Date: May 2009
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Ok...let's take these one topic at a time...

First of Bostik's Best does not have a moisture barrier in it. It is a full-urethane adhesive, so does have some degree of resistance to moisture and alkali, but it in itself is not intended to provide protection.

Right now, start off with getting a more accurate moisture test. Meters are good at pinpointing problem areas, but can't be trusted for accuracy. Ideally, you should have a calcium chloride test Calcium Chloride Moisture Test Kit to determine what kind of emission rate we're dealing with.

To get moisture that high, most likely you have a high water table under the property and no barrier/damaged barrier beneath the slab. It's also possible that there was some kind of plumbing leak beneath,maybe even sewer lines, but it sounds like you already checked for that.

You definitely don't want to do anything with flooring until you can correct the moisture. And you can't know which sealer will or won't be effective until you get an accurte reading of the moisture emission rate. Different products are effective at different levels.

I would definitely steer you toward floating the next floor. Tht will allow you to seal the slab, install a sheet barrier (6 mil poly or the like), and then the floor.
Old 11-13-09, 05:41 PM
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Thanks guys! This isn't actually for a basement unfortunately. It's throughout the main floor (we don't have basements here). That building science website was VERY interesting.

So the flooring company is coming out to remove all the extra adhesive that may be on the floor tomorrow. I saw somewhere that may alter the readings. Then I'm gonna have the calcium chloride test done sometime next week (give the floor a couple days to breathe with nothing on it).

Flooring company told me to put down something by Mohawk Flooring called the "Pro-Tech M901 Wood Flooring Membrane for Moisture Reduction." I've also seen the "Bostik MVP4" which is what Home Depot said to use and supposedly works with the Bostik Best Adhesive to provide a sound seal. In doing some reading I found either of those (Mohawk or Bostik) will protect the floor from moisture in the concrete up to 25 lbs for Mohawk or 21 lbs for Bostick. So here's hoping the calcium chloride test comes back at less then that. If it doesn't....I dunno what to do.

Floor Company still says they want to glue down and if we use either of those products there is apparently a warranty if we glue down also. I dunno. At this point I feel more knowledgeable than the flooring company - which is scary. THEY DIDN'T EVEN KNOW WHAT A CALCIUM CHLORIDE TEST IS! ((sigh))

We had gutters installed in May, I'm wondering if the last 12 years of the previous owner not having them made a difference. Landscaping is directing the flow of water away from the house. No idea what the water table depth is? Umm we've had a LOT of rain over the past couple months, none in the past couple weeks but about 6 weeks straight through Sept./mid Oct. We've gotten more rain this year than we have in like the last 5 years. Maybe that has something to do with it? I dunno. Crossing fingers for a low read on the CC test...
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