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I inherited an interior perimeter drain with a sump-pump as part of a basement waterproofing system when I purchased my new home two years ago.

Since then I have noticed that along the seam of the drain, where the concrete covering the drain system meets the basement slab, the concrete always appears to be darker in color than the rest of the floor and always has a damp feel to it.

The perimeter drain company says this is due to condensation. It would seem to me that if the drain is functioning properly then there should be little condensation occurring.

Does anyone have experience with these types of systems and know what I should be expecting as far as performance and dryness?

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If possible, you could try taping some 6mil vapor barrier down over top of it. You just need a small square (maybe 1'x1') that is air tight (and don't leave a pocket of air underneath, as much as possible). If you are getting moisture up through the concrete, it will be damp underneath the plastic. If it's condensation (the humid air in your house condensing on the cold concrete) there will be condensation on the top/outside of the plastic. –  gregmac Sep 1 '11 at 6:29
    
I do notice when I run a dehumidified the amount of damp concrete appears less than when I don't run one. I can't tell from that if the water being removed is coming from the air or the ground. I'll give this technique a try. –  Chris Heller Dec 22 '11 at 16:20
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Ideally, the builder installed a vapor barrier under the whole slab including the drain but it sounds like they cut a hole in the barrier to dig the pit for the sump. Since concrete is fairly porous, it's probably wicking water from the ground. If it bothers you, try a sealer intended for concrete with your problem. Unfortunately, you can't tell how much pressure the water is under because it evaporates or runs into the sump. Although it shouldn't be much, it will still wreak havoc with surface coatings.

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I am only bothered if the dampness is caused by a failing drain system and not natural moisture. I'd rather not use a sealant, since as you note, there is really no stopping water! –  Chris Heller Dec 22 '11 at 16:21
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