Mildew on plaster/concrete wall


Old 01-14-05, 02:56 PM
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Mildew on plaster/concrete wall


Our 2-story home is made of poured concrete. The interior finished walls consist of about 1/4 inch of plaster adhered directly to the concrete (no insulation). We're having trouble with the plaster coming loose from the concrete and also mildew on the plaster during the winter. Do you think a vapor barrier paint would be the solution? We live in Pennsylvania so we do have cold winters. Our home is small so putting studs in isn't an option because of space limitations.

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Old 01-17-05, 08:08 PM
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I'm not sure if it will help or not, the plaster coming off seems to be a moisture problem, but might not. Is it new plaster, or the old coming off?

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Hy-Tech insulating paint
Old 01-18-05, 05:00 AM
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Moisture wicking inside through concrete could cause plaster to spall off walls. High humidity indoors could also contribute to damp plaster. I have the same problem at my store. Moisture is wicking in through old cinder block that needs a couple coats of exterior paint. The problem with the waterproofing products is that they can not be used over painted surfaces.
Old 01-18-05, 09:22 PM
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I have seen gypsum plaster over poured concrete come loose after years. I'm pretty sure that it's from moisture wicking through the wall from outside. I don't think a vapor barrier paint between the concrete and plaster is a solution. The moisture will still wick through and hit the piant and something has to give and it's probabaly the paint and what ever is on top of it. Years ago when I worked in Hays, Kansas I did a few patches at the university that were some kind of black tarry stuff on the blocks and plaster on top of that. After about 40 years some came loose. The plaster was pretty good but the bond failed. I think that was from moisture. What I did was nail metal lath to the blocks and plastered it. Of course if there is still moisture coming through eventually the nails will rust and the whole thing could come loose. I'm banking on another fifty years, though.

reposted per author's permission.

Bottom line, you;ve got to eliminate the moisture problems in the wall or the mold & crumbling plaster will only get worse. Options are attach lath & replaster or attach stud & drywall.
Old 01-19-05, 02:16 PM
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Yes, I think it is moisture

I think so because our storm windows are now foggy so there must be moisture somewhere. I just spoke to a masonry contractor who suggested that the problem is because of the lack of insulation between the poured concrete (not block) and the plaster topcoat, which is only about 2/8 inches thick. He suggested putting 3/8" lathe on the concrete and then using foil as an insulator between the concrete and interior wall in order to conserve space. Do they make such a thing as foil-backed drywall?
Old 01-19-05, 02:44 PM
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He must be talking about putting that on the wall, then the lath and new plaster. No foil backed drywall products I'm aware of.
Old 01-19-05, 07:30 PM
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I'm not sure this adds up. Do you intend to put 3/8 gypaum lath on the wall? Fur it out with 3/8 wood lath? Where will the foil be? Next to the concrete or inside? How will you finish the foil? What I am concerned about is that you won't have any insulation unless you use some real insulation. If you don't have insulation I don't see how you are going to solve your problem. In fact you are just making more places for condensation to form and soak more material. You could use some foam but it may violate codes on an interior space. They do make foil backed foam. I think I have seen foil backed drywall or maybe foil backed gypsum lath.
Here is a different approach:
What is the exterior finish of the house? Is it poured concrete on the outside perhaps with a stucco finish for decoration? If so you might consider an Exterior Insulating Finish System (EIFS). Probabaly the best known brand is DRYVIT. Those sytems are expensive but they look good and those issues with moisture penetration are not relevant on poured concrete. This will give you insulation, a new exterior finish, will not disrupt anything on the inside and will not demand any sacrifice or room in the house.

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