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Old 05-10-2010, 01:49 PM   #1
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Concrete Slab Sweating and Best Floor To Install


I have had one heck of a time. I have a 250 square foot area in my home that I need to address. It is a concrete slab in my air conditioned home. I had bamboo wood installed about two years ago and due to faulty installation and moisture, the floor buckled expanded and developed mold/fungus underneath. I have had the wood floor removed and all the glue scraped. I now have a clean concrete slab with which to start with. Here are the issues:

1. I have had my air conditioning off and we have moved from spring to humid summer (Charleston, SC) and I am having concrete slab sweating. The slab was put down in 1978 and does not have a vapor barrier below it so I might have had a little bit of foundation seepage as well.

2. This is a townhouse and will eventually become a rental property. The room of interest is a living room and a major thoroughfare between the front door and the stairs to the second level. So, I do not want to invest a lot of money. I just lost about $1000 on the wood floor job.

2. I do not want to put wood back down for fear that I will have this moisture problem again.

3. I do not like carpet but it is favorable because it is the cheapest option. However, who is to say that moisture is not going to develop underneath it and allow for mold and fungus growth?

4. I do like tile but the installation is too expensive and I cannot afford it.

5. I do not know anything about cork but I would think that it would have the same problem with the moisture.

6. A knowledgeable friend suggested I stain the concrete slab and go with that. However, I do not know whether I can do this despite the moisture or if there is something I can seal the slab with and then come back and stain it.

So all in all, what absolutely must be done to deal with the foundation seepage (if any) and slab sweating when I like to have my doors and windows open in the slightly humid spring?

Then, after the seepage and sweating is dealt with, what are my best flooring options?

Thank you,
DuBose Griffin
Charleston, SC
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Old 05-10-2010, 02:07 PM   #2
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First, find out which it is: Tape a 2 foot square of clear plastic to the floor, sealing all four sides with duct tape. Wait 2 days and see if the moisture is on top of bottom of the plastic.
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Old 05-10-2010, 02:31 PM   #3
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I assume I should do this over a period when it is humid and I have the ac off. We had a very humid week and then we have been cool again with low humidity. Also, several months ago we had a lot of rain which could have raised the ground level not to mention I am in coastal area with a high water table.

Ultimately, my question is if their is foundation seepage and it is related to high water tables or excessive rain, how would I capture this in two days if we are in a dry spell?

Also, I should have mentioned in my first post that the water on the surface of the concrete in consistent areas of the concrete but does not cover the entire floor.

It seems that this two day test could positively confirm sweating but not completely rule out seepage.

Thank you,
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Old 05-10-2010, 03:47 PM   #4
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Welcome, DuBose.

We need to nail down some terminology so's we can separate the apples from the oranges as Injineer Bob is suggesting.

Finding moisture on the surface of your concrete SOG would be consistent with condensation. That can occur only if the surface of the concrete is at or below the dew-point temperature of the air inside the room in question. That would not be a slab problem, even though you indicate your slab was not properly prepared before placement.

A second source of liquid moisture at the slab surface could be from hydrostatic pressure forcing liquid moisture to the surface. That would be a very serious problem and would eliminate the successful installation of most any floor covering. Treatment of that kinda problem would involve landscaping and other exterior considerations.

Third, and not at all likely to result in liquid moisture appearing on the surface under the conditions you describe would be moisture vapor transmission from below. You will almost certainly have some of that due to your lack of a vapor barrier under the concrete. The extent of it is what Bob's test will help you determine. This condition should be more evident when the interior of the structure is being cooled artificially, though, and the results might be misleading unless conducted during those conditions. But if such a test does indicate vapor transmission when the interior is also warm and moist, you can expect a much more dramatic indication when the room is cool and dry.

What you need to determine is which of these things is makin' the wet spots, eh?

My opinion; worth price charged.

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