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We recently built a house on a cement slab. Half of the first floor is a garage and the other half is a rec room. I’ve noticed what looks like condensaton. The cement is damp in patches which come and go for no apparent reason. I purchased a de-humidifer which helps. However, when I ask the builder if he installed a vapor barrier under the concrete pad he said “No we never do that here”.
Is it possible to correct this situation by installing a plastic vapor barrier over the top of the concrete and laying a new floor of some kind over that? Any suggestions will be much appreciated.
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Mr. Smith,
Where is "here"?
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Yes you can. I believe PERGO and some Bruce Flooring can be installed over concrete with a plastic (6 mil+) vapor barrier. The flooring is edge glued and "floats" over the plastic. The alternative is to lay plastic and then apply wooden lath over the plastic.
OR . . . Has anyone tried a concrete sealer like UGL Drylock under carpet??
*Steve,"here" is in Michigan's upper penninsula, 400' from Lake Michigan. The home faces south to the lake. This practice may be limited to my builder as I have not had the time to check with others. This is a second home for us where we spend a couple weekends a month and some time in the summer. Thanks for the response. Roger Smith
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Tedford; I used Drylok (the latex based variety) on concrete block walls, but there is still a lot of efflorescence coming through and lifting the Drylok. Maybe it's better than nothing, but I wouldn't recommend it to anyone.
RB; I would be leery of putting down a vapor barrier on top of the concrete. A few years ago I had a leftover piece of vinyl flooring about 10 ft square, so I just spread it out on our concrete basement floor to dress up an area at the bottom of the stairs. A month or so later I began to notice a musty smell, so I lifted up a corner of this vinyl and it was just simply floating on a film of water. Moisture was working its way up through the concrete, but couldn't evaporate with the vinyl on top of it. The remainder of the basement floor was probably letting just as much moisture pass through, but being uncovered it was evaporating as fast as it came through.
Anyway, if you put down a plastic barrier then flooring of any kind (carpet or wood) I think you might have the same problem with moisture trapped below and possibly causing no end of mold and mildew problems.
*Roger,It is possible, of course, that the moisture in your slab is wicking up from the ground below. Another possibility is condensation from humid lake air. Before I would invest in a concrete sealer I would tape down some plastic sheeting. If water collects under the plastic the problem is migration from below. If, however, the concrete is dry and uncoverd areas are damp the problem is condensation. The best cure for that is carpet.
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Should a vapor barrier be installed in the attic prior to blowing in celulose insulation?
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Hi Gray,
If the cells are being blown in loose rather than dense-packed in a closed cavity, a vapor barrier should be used. Most important is that the ceiling plane be as air-tight as possible, since most moisture migrates via air-movement, not diffusion.
Steve
*Hey Steve,I have got 4-5 inches of cellulose laying on top of a plaster and lath ceiling which is in pretty good shape. Can I just blow about another 12 inches of cellulose on top of the existing material? The existing material appears to have been there forever or at least since the "20's or so when the house was built.Thanks,Stephen
*Hi Stephen,Sure you can, but first I would inspect every inch of the ceiling from the attic side and plug any concievable air passage with expanding foam. For penetrations that need a fire break--like a chimney--constuct a metal collar to seal it up and seal it up good with fire-rated calk. If you have recessed lights--if they are IC rated--build a drywall box around them and seal all the joints, then pour on the cellulose. If they are not IC rated, do not do this, as it will be a fire hazard. I would replace non-IC units with air-sealed units available from Juno, which elimates the need to box them in.Steve
*Dont know about michigan but a vapor barrier is required by code here in SC if the slab is for a living space.
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We recently built a house on a cement slab. Half of the first floor is a garage and the other half is a rec room. I've noticed what looks like condensaton. The cement is damp in patches which come and go for no apparent reason. I purchased a de-humidifer which helps. However, when I ask the builder if he installed a vapor barrier under the concrete pad he said "No we never do that here".
Is it possible to correct this situation by installing a plastic vapor barrier over the top of the concrete and laying a new floor of some kind over that? Any suggestions will be much appreciated.