Is it mildew or termites? I am unable to tell from the picture.

It does look like mold. You want to make sure the wall isn't rotting out from water damage and get it fixed ASAP if it is.

You can clean it with a water/bleach/TSP mixture let it dry out, wait a year, and check it again. IF the mold grows back, you have mold in the wall.

If that is a slab floor, the slab should be damp if it is mold/mildew. If not, wipe and see if the black comes off as it could be termites. If it is termites, then you most likely have both wet walls and floors as that is what produces the climate for termites.

duplicate post

This post was edited by patricia43 on Thu, Jun 12, 14 at 18:39

It would not allow me to edit the duplicate post. Sorry.

What's on the other side of the wall? If outside, is there a downspout (could be loose) or rainwater that stays against or goes towards the house? If it's an interior wall (with room on the other side), is there a pipe in the wall? I would pull off the baseboard and look behind it. Water or termites, it has to be repaired.

So it's an outside wall, I think I have to take some drywall down, see what's going on. It's dry as can be around the floor, window etc. It's a wood floor, we have a bungalow with a basement. I think it's mold :(

The first thing to do would be to pull back the carpet. That will tell you if the floor is wet. I would probably them pull of that baseboard strip -- if the wood is still sound, you may clean it up and replace it or just replace with new. There should be a gap between the drywall and the floor. I would look for moisture there. before tearing into the wall, I would follow anything you see up and look for possible damage above -- water stains, loose tape joints, any swelling or buckling. Look up and see what possible sources are above as well as outside (sprinkler head, pooling water, etc.). If you can determine the area of the source, you may not need to do as much damage to the wall that will all have to be repaired.

Is there a bathroom above? a water line that runs across? Hot water heater or AC drain overflow that could have backed up? See what you can about those potential sources from above and outside and see if you can save yourself some work and money. We discovered a problem the previous owners covered up with paint when we removed a baseboard to put down new flooring. It came from the upstairs bathroom, but only the baseboard needed to be replaced and everything else cleaned up fine. .