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Question DetailsAsked on 8/23/2017

What should I do about a damp floor?

My house was built in 1958, with an addition that was put on in 1970. The room I am concerned about is in the addition. The person who put the addition on should have had their tools taken away. Instead of putting down a vapor barrier before they laid the concrete for the floor, they did not. As a result moisture seeps up through the concrete, through the asbestos tile and has made this room damp. We run a dehumidifier 24/7. In 1989 my father put down commercial grade, rubber backed carpet tile, which he thought was going to solve the issue. Now I have mold/mildew. I want to take up the carpet, and paint the tile with a basement floor sealer to combat the moisture. Will this work? (I know the mold has to be cleaned with bleach, hot water, and elbow grease)

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Here are links to some previous similar questions which might help FYI -

If the concrete is actually wet, generally without externally blocking/intercepting the water (like keeping roof runoff away from the foundation or with an exterior french drain system) or putting in an underdrain system leading to a sump pump to keep the water level significantly below the concrete, other than a few water-cure underwater epoxy type products there is not really anything you can put down and expect to work.

if just damp, there are some water cure higher-end concrete surfacing finishes which also seal fairly good against water vapro transmission (NOT against actual water pressure forcing its way through), and with proper pre-drying to remove free water tile and stone flooring can also be put down using portland plastic cement mudcoat/thinset. (Not really plastic containing but called that).

"Paint" as such, including pretty much all the one-component basement "waterproofing" paints and grouts, is pretty ineffective against actual water intrusion (as opposed to just water vapor transmission). Most of them, at best, act like a grout to reduce leakage through cracks and voids and porous concrete block - basically speaking negative side (the side away from the water source) treatment is of marginal effectiveness at best - as you indicated about putting VB down BEFORE the slab, positive (water source side) blockage is much mnore effective,and can also use materials like loose plastic sheeting and bitumastic sealants or sheeting which are not acceptable on the interior of the house.

For a slightly damp slab SOMETIMES you can get away with a 6 mil or thicker vapor barrier fully caulked (and sometimes batten strip fastened) around the edges, with padding and flooring materials over that. But if the moisture ever escapes (say groundwater level increases or more water gets in under the footings) then you get mold and wet flooring. Also, you will commonly get some mold on the concrete under the vapor barrier (though a good bleaching first and then sprinkling borax powder over the concrete before putting the vapor barrier down commonly suppresses that pretty well), so if the vapor barrier does not stay tightly sealed or is in contact with wood at the perimeter (which it should not be) you can get odors. Ditto from stagnant water under the VB - can smell like a swamp, so not a solution I recommend.

You can find a LOT of previous questions with answers and ranges of solutions (both preventative water control, and active drainage/dewatering systems) - look in the Basement Waterproofing link under Browse Projects,, at lower left. Note the preventative measure are preferred - both because they generally are better at keeping the slab dry, but also generally they have greater tolerance of higher influx of water from elevated groundwater or heavy rains or snowmelt or overflowing gutters and such.

And of course, for any remediation solution you consider, assuming this asbestos tile is old (so the hazardous material type of asbestos - which can be confirmed or ruled out by test kit), you may have the added cost of its removal.

Answered 3 years ago by LCD

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