-1 Helpful?

What are the best sealers for concrete block walls and concrete slab floors, when applied from the inside.

As noted in the webinar, stopping moisture at the outside face of an assembly is always best, but for older (1950's & 60's era) concrete block walls and concrete slab floors below grade, what type of sealer products or other techniques work best to try to prevent moisture penetration, and subsequent musty smells? Thank you.

Asked by Anonymous
Posted Dec 21, 2009 5:09 PM ET


6 Answers

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If your basement walls are damp or moving a lot of moisture in the form of vapor into the basement, I have yet to find anything other than a good dehumidifier that can handle this moisture migration. Sealers applied to the interior, trying to deal with moisture that is already in the wall, just don't seem to work. They certainly are no solution if you have liquid water coming in through the slab or walls. You do pay the energy penalty for the dehumidifier, but if you find a sealer that works on the interior, please let us all know. Mike, you have a different answer on this one?

Answered by Peter Yost
Posted Dec 21, 2009 9:08 PM ET


What about 2" of closed cell spray foam applied to the interior? Like Peter explained, nothing will protect from heavy amounts of liquid water coming in from the exterior, but I would assume that closed cell foam would prevent minor moisture migration.
Peter, Mike, Martin... your thoughts?

Answered by Brett Moyer
Posted Dec 21, 2009 10:54 PM ET


I agree with you.

Answered by Martin Holladay, GBA Advisor
Posted Dec 22, 2009 6:46 AM ET


Spray foam is an expensive solution, though it will offer insulation benefits as well, but it may have to be covered with a fire-resistant layer.

A simpler alternative is to paint on two coats of UGL Drylock latex masonry sealer. I use it for exterior foundation waterproofing and even for swimming pools. The manufacturer claims it can withstand 10 lbs of hydrostatic pressure (22 ft. of head).


Answered by Riversong
Posted Dec 22, 2009 3:31 PM ET


I have tried and had mixed success with the UGL and other concrete sealing products. Success on relatively new, clean (no effervescence, dirt, dust or other coating ) has been good but I never use in areas that will be covered. Once you cover it, you can't see it and take any additional remediation should it not work.

I agree w/ James and Martin that closed cell foam is best solution at this point.

There are other systems you can retrofit that will create a drainage barrier at the concrete face that lead to a water collection system along the slab. Time consuming and costly (due to labor) it seems. These make spray foam seem affordable.

Answered by Mike Guertin, GBA Advisor
Posted Jan 1, 2010 4:56 PM ET


Again, spray foam will have to be protected by a 15 minute fire resistant material.

For the floor, I would use a urethane-based floor enamel, two coats.

Answered by Riversong
Posted Jan 1, 2010 8:32 PM ET

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