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dampness/ water table

Posted by kennebunker (My Page) on
Sun, Oct 1, 06 at 16:00

We've never had anything actually wet in our basement, but the humidity level is always high, @80%. The concrete floor has dark gray areas, and whenever anything sits on the floor for a few weeks, the floor underneath looks lighter when you remove the object.
The house is 9 years old, and was built a bit higher than our neighbors' because the water table is only 6-8 inches below our concrete basement floor.
Last year DH bought a dehumidifier which runs constantly, but it seems to me that the floor looks damper now than it did before. Could it be that while the dehumidifier is pulling water out of the air it's being constantly replaced from the endless supply of groundwater under the house?
If I'm right about the humidity levels being constantly replenished from the ground water,I'm thinking that perhaps the waterproofing/radon seal might be the wiser course than constantly running the dehumidifier. DH however, hates to spend $800 to buy enough of the radon seal we need for our big basement. We bought a radon pump a few years ago,because we discovered our radon level was slightly above acceptable levels, but I only run it during the night when we're asleep. I hate listening to the darn thing run all day long. I've found that my next door neighbors got tired of listening to theirs too.
Am I right about the water replenishment?
Has anyone else experience with the radon/waterseal product?

Follow-Up Postings:

RE: dampness/ water table

quote-"and whenever anything sits on the floor for a few weeks, the floor underneath looks lighter when you remove the object."

If the floor is lighter under the object that means it is drier there.

Next time you watch your local weather report pay attention to the "DEW POINT". Dew Point always equal to or less than your air temperature and it is the temperature at which precipitation will occur based upon the percent of moisture (humidty) in the air. If the actual temperature of the surface of the concrete is cooler than the dew point the humidity in the air is condensing on the concrete producing the moisture therefore it is not a leaking through the floor from underneath.

RE: dampness/ water table

That's what I would logically think, but I remember hearing the exact opposite on some home improvement show years ago, that oddly enough dry spots under things on the floor meant it was coming through the floor.
I had a basement where I had to throw out somethings because of mold and mildew that accumulated on them while they were stored, but I never had damp looking areas on the floor. The basement in question in that case never seemed damp at all.
This one always seems damp, but in 9 years I've never seen any mold or mildew in the basement. Of course, now that I've said that, I'll go down there tommorrow and find some.

There's got to be a better solution than running the dehumidifier all day every day for most of the year. It's not like I live in a humid tropical climate.

RE: dampness/ water table

If you heard the opposite to what I told you on a home improvement show I would have serious resevation about trusting their improvement information. In fact, before they lay ceramic tile on concrete they perform a test to determine if moisture is coming through the concrete. To perform the test you lay a rubber matt on the floor for 24 to 48 hours, then lift the matt and see if there is a a dark area or evidence of moisture. If so, you must apply a concrete sealer before installing tile.

While you may not live in a humid tropical climate it must be remembered that the floor of a basement is typically 6' to 8' below average grade, which means the underside of the slab is constantly at the average earth geothermal temperature of 50 to 55degF which then leaves the top of the floor surface at an average of about 60degF which is generally well below the average summeer dew point in even drier climates.

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