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I have a northwest facing wall in my home that I have just discovered has damp and slightly mildewed drywall on the bottom 10-12 inches. When I cut out a piece to see what the problem was I discovered that the drywall was placed against the cement foundation. There is a thin piece of poly between the foundation and the drywall and there is moisture on the inside of the poly. How do I fix this problem?
thanks
Tris
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You probably can't. Assuming you live in a cold climate, vapor barrier (the plastic) has to be on the 'warm side' of insulation. Because the drywall is against the concrete foundation (the 'cold side') water vapor is going through the drywall and changing to liquid once it hits the cold plastic.
The best thing to do is to more or less build an insulated wall against the foundation and fasten the drywall to that. Even 1" of styrofoam would probably do, but I'd do better. Think of the energy savings.
If you don't want to do that, you might look into vapor barrier paints, which would at least form a vapor barrier on the warm side. I don't know for sure if it would work, but I would give it a try. Of course, then you'd have two vapor barriers, which isn't kosher.
*Thanks Brian. So far I have removed the drywall from the bottom of the wall up approx. 12 inches. If I put 2x2's against the foundation with styrofoam between them so that the 2x2's are just above the foundation and then put the poly and drywall over that (creating a small ledge along the wall) will that be enough? I'm not concerned about the ledge because I will be installing some built in cabinets along the wall.Thanks again, Tris
*The moisture on the warm side of the poly would sure suggest inside warm air condensing on the cold plastic. However, you have looked hard to see there's no water entry from the outside? Check it all before you cover it up. Best of luck.
*Probably 2 x 2s would do, but I would go for 2 x 3s or the classic, 2 x 4s. I find 2x2 too unstable & they tend to split when you fasten them to things. I would do the whole wall, rather than just the bottom, because doing just part may simply move the problem. Calvin's comment is correct, and yes you should make sure no moisture is coming through the wall, although it could be the same effect - condensing due to the temperature change. So, even if you stem moisture coming in from the outside, I would insulate the wall and put a vapour barrier on the warm side, or expect the drywall to disintegrate with time.Good luck!
*Five will get you Ten that the slab is wicking moisture into the drywall. Switch to nice high baseboard and re-attach the drywall above the slab. Seal the ends of the drywall with silicone calk. Fir out the bottom of the studs with 1/2". Re-attach the baseboard.
*Thanks guys for all your help. I checked for moisture coming through the slab and foundation by duct taping poly at different locations. No moisture coming through so I've gone ahead and built a "2nd" insulated wall. The room is already warmer. Thanks again. I really appreciate your inputTris
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I have a northwest facing wall in my home that I have just discovered has damp and slightly mildewed drywall on the bottom 10-12 inches. When I cut out a piece to see what the problem was I discovered that the drywall was placed against the cement foundation. There is a thin piece of poly between the foundation and the drywall and there is moisture on the inside of the poly. How do I fix this problem?
thanks
Tris