Damp Concrete Floor

4 Apr 2009
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United Kingdom
Can some helpful person please give me some expert advice. When I come home at night after being out for several hours, I often (but not always) notice a musty/stale smell immediately inside the front door of my 1978 bungalow. I pulled back carpet and underlay (laid only 3 years ago) and notice that the concrete floor looks damp and the underlay smelt damp. I cleaned it off, dried the floor with a hair dryer, hoping this would solve the problem. I even put a piece of kitchen roll under the underlay but it REALLY smelt when I took it up after just a few hours. I've now stuck a piece of polythene down to check for damp. My question is, is there something I can paint on this section of concrete floor to solve this problem, or will the damp just come up somewhere else? I don't want to have to get someone to dig up the floor if there's another solution. There is no evidence of damp in the walls, just this section of floor inside the front door. Any help and/or advice gratefully accepted by this diy female. Jubbly
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There is a product called Aquaseal which, when painted on, could give the fix you need - however the real way is to have the concrete dug out, a membrane fitted and then reconcreted. Do you suspect a high water table in your area, or is there a possibility of a leaking heating pipe down there? Could rainwater be blowing in under the door? Cheers John
I think that you would be better finding out the cause of the damp before you try and seal it in.
Aquaseal is quite good, and has fibre strands in it, Liquid Rubber is better as it is water based and can be spread on damp surfaces. BUT the damp is coming from somewhere and need stopping, concrete will eventially fail. :confused:
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Before going to any drastic measures, the first action should be to temporarily remove the carpet/underlay/plastic sheeting for say 2-4 weeks and see if the oversite concrete dries out, as the problem could be related to water vapour becoming trapped between the underlay and concrete slab which then condensates out and reacts with the underlay (or more commonly the reaction is with any adhesive that may have been used to stick the underlay down) which then generates a rather musky sometimes pungent smell, like bad eggs (ammonia).
If the concrete dries out then you will know that you have a problem with vapour penetration - now things become a little more complicated, in that you will need to find the cause of the dampness, which could be anything from a leaking copper pipe to breach of the damp proof membrane, or a lack of thermal insulation which is causing thermal bridging (which will cause similar problems) regretfully the only real solution would be to take up a small section of the floor starting at the worst affected area then working backwards section by section until a cause is found.

An alternative proposition rather than a solution, but far less disruptive would be to replace the carpet with clay quarry tiles laid on a sand and cement bedding, although not getting rid of the problem this proposal would allow the floor to breathe, any water vapour being released should be minimal and after a while any left over smells should become unnoticeable.

Simple really, inside the front door? your doors not weather proof and letting in water.

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