How can I fix a small slightly damp area in my basement wall?

Question

I am in the process of converting a bedroom in our walkout basement, into an office. Back in 1999, the previous owner had finished the basement. The basement foundation walls are hollow cinder block, and there have been no water problems anywhere in the basement with the exception of this one corner of the room we are renovating. There have been some issues with mold/damp drywall in that corner for quite a while.

I just opened the walls (drywalled studded walls, about 1" in from the cinder block), and found a 4-foot section with damp cinder block going approximately 6-inches up off the slab (above 6-inches up, all is dry). In the previous basement finishing, poly was placed against the cinder block wall, a 1" space was left, then a studded interior wall was put up, filled with fiberglass insulation, then drywalled.

It looks like there is quite a bit of condensation on the insulation side of the poly, which is creating dampness, and is getting through to the drywall.

Any thoughts on how I might fix this problem.

Answer 1

Water IS getting to it. There IS water there. You cannot fix it by covering the wet. You must fix it by stopping the water from getting to that point.

Check your gutters. Do they tend to get clogged? Are the downspouts set so the water is directed away from that area?

Check the grading in that area.

If all of this checks out, then the water is getting through the wall. There may be a crack. You may need to dig down and apply water proofing in that area, or repair the crack.

Answer 2

Well, it turns out that it wasn't water coming through the foundation wall. Right above the area in question is the main service panel for the house. Water was slowly seeping in through the conduit, and actually into the breaker box itself (eek!). It was then dripping down through the insulation, and along the poly.

An electrician friend has seen this happen quite often, and is coming over tomorrow to fix it. (I have since taken a blow dryer and dried out the breaker box, and as there is significant corrosion inside, will be replacing it)

Answer 3

Poly is almost NEVER a good solution for the interior structure of a habitable, heated building.

As you've seen, the insulation was insufficient for preventing moisture laden air from reaching the dewpoint at the poly. Whether the dampness is coming through the block or from the interior to the poly.

See this answer, regarding use of XPS insulation and not using poly on the interior side.

Put poly outside, as in under the slab or outside a drainage plane along the basement wall (on the outside).