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We purchased a 3000 square foot ranch that was built in 1977. We would like to finish about 1000 sf of the basement. It has poured concrete walls and a concrete floor. Currently, we have two sump pumps, one at each corner of the house. They were put in separately and do not connect. We do not have standing water, just issues when we leave things sitting on the concrete floor. A cardboard box will result with some mold underneath. Carpet tile with a rubber backing will cause some molding, efflorescence, and lime deposits to appear. The efflorescence shows up in random spots throughout the basement whether they are covered with something or not. Sometimes the basement smells musty, and sometimes not. We run a dehumidifier.

We were looking at using a subfloor system such as DRIcore interlocking tiles or Delta - FL to lay under an interlocking floating waterproof flooring material. We purchased a few pieces of the DRIcore to test an area and after a couple of weeks, we removed the pieces and the concrete floor underneath was darker and damp.

We were thinking of having our landscaper dig down to find the exterior drainage tile at the corner of the house to verify that it exists and to see if it is clogged. But then what?

We called a waterproofing contractor and he recommended finishing the interior perimeter drain tile in the basement to connect the two sump pumps. We are waiting on his bid.

Not sure what to do first or where to spend the money. Will finishing the interior perimeter drain tile work? Shall we cross the drain tile at the center of the basement? What will this do to the structural integrity of the concrete floor? We would appreciate any advice that you all may have.

  • With a poured floor and walls I would want to put exterior drainage in and pump the water from outside. There are 2 part epoxi coatings that do a wonderful job of sealing. I had a basement much like yours winter months we pulled gallons of water water from our dehumidifier. After painting the floor the moisture problem was almost gone. Some types require a dry floor and may need to be done in summer months but getting the water away from the walls and floor would be the first step in any plan. – Ed Beal Sep 12 '17 at 1:56
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    FWIW, minor dampness is not the same as hydrostatic pressure, and the solutions tend to be different. – isherwood Sep 12 '17 at 17:58
  • I think we are going to test the moisture content in our concrete slab. Maybe go ahead and add interior perimeter drains to connect our two sump pumps and then test the slab again. – Paulette Sep 14 '17 at 22:34
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Do your sump pumps run frequently during wet weather? Does water leak through any cracks in the walls or floor? Do you get puddling or standing water in any area of the basement during heavy rains? Do you have an extremely high water table in the area?

If not, I suspect your problem is normal ground moisture not necessarily drainage water or the water table. The developer that built the house or contractor that poured the floor is responsible for not putting down a vapor barrier.

I would propose that amongst the other things you are investigating, you have a small section (maybe 1' x 1') of flooring saw cut and removed to look underneath the floor. This could be done in an area that will not be finished and could be a DIY project costing you less than $100. Or hired done for a couple hundred dollars. There should be a layer of heavy plastic under the concrete floor. (You could also leave this open to see if water puddles in the hole.)

If your basement floor does NOT have a vapor barrier under it, I propose all these other things will come to naught. If you are getting moisture leeching through the concrete floor then I don't think perimeter drainage is your problem.

The best solution would then be removing as much of the basement floor as possible and have the concrete replaced with a heavy plastic vapor barrier underneath.

Ultimately, if you finish the basement without entirely solving the moisture issue, I would recommend you never use carpeting. Paint on the basement floor may not hold. Therefore, check into just staining the concrete and leaving it after that if you want some color to the floor. This will still allow it to breathe. Throw rugs or anything else that is absorbent, on the floor will promote mold. You will need a dehumidifier running in most weather except for the very driest weather.

Good luck!

  • Waterproofing from the outside (coating the walls, vapor barrier under the floor) is clearly the best solution, but it's really expensive to retrofit. What about waterproofing coatings that might be applied on the interior (drylok and others)? Are those not viable solutions to vapor infiltration? – Shimon Rura Sep 12 '17 at 17:11
  • If the vapor is coming through the floor you would have to paint the floor with Drylok. Not a pretty sight. It could be done but probably not acceptable to most people. – ArchonOSX Sep 13 '17 at 8:41

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