Moisture High In Slab - Flooring - DIY Chatroom Home Improvement Forum

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Old 11-12-2009, 05:00 PM   #1
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Moisture high in slab

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 recently 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 like they should have). 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 11-12-2009, 06:26 PM   #2
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Sounds like an underground spring or clay soil feeding surrounding water to you. Solution, Fig. 1, 2, or 3:
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Old 11-12-2009, 06:57 PM   #3
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In cases like this, a sump pump would solve the problem, have one dug...or have a contractor drill a 3" diameter hole through the concrete right down about a foot to see what's going on there. Then have someone take a X-ray look a the whole floor.
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Old 11-13-2009, 06:47 AM   #4
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Sounds like the concrete was poured on top of soil without a sufficient gravel base under it. Concrete is a sponge. It will absorb moisture out of the ground easily. Your best bet at this point may be to lay an impervious moisture barrier on the slab, sealing all joints, and install sleepers over it. Then install wood flooring over the sleepers. An impervious coating is likely to lift from vapor pressure. A quick and dirty way to test is to tape a 2'x2' piece of 6 mil poly to the floor. After 2-3 days look at the concrete and the bottom of the poly to see if any visible moisture is present.
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Old 11-13-2009, 05:37 PM   #5
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If your slab is experiencing "rising moisture" then there is NO WAY to seal it from above. Many people will tell you to use their coatings but the truth is...they won't work for long.

What is the depth of the water table in your area?

Is your landscaping designed to direct water AWAY from the dwelling?

Are you gutters and downspouts installed and working properly?

M6 may be on the right track in this case.
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Old 11-13-2009, 07:27 PM   #6
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Thanks! 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. 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. In doing some reading I found either of those will protect the floor from moisture in the concrete up to 25 lbs. So here's hoping the calcium chloride test comes back at less then that. If it doesn't....I dunno what to do.

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. Thanks for the ideas!


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