I'm re-finishing a room in my side-split. It is in the "upper basemnt" level (about 1/2 underground). I noticed that on the two outside walls there is a slight separation (about max 1/8") where the floor slab meets the wall.
In this area there is some whitish staining and some deterioration at one point. There were 2x4 walls installed with the bottom plates tight against this area...they were not rotten but smelled a little musty in some areas. They were probably there for a good 25 years.
I'm going to be intalling 2" XPS against the concrete wall and have either sill gasket or caulking under the XPS where it meets the floor. Should I be sealing this corner area? If so, with what? No water is present that I can see even after rain and show melt.
It's normal to have that gap.
Is the bottom plate pressure treated?
Have you been running a dehumdifyer?
The staining sounds like moisture seeping through the wall from the outside.
Gutters, grade sloping away from the foundation, no mulch piled up againt the foundation, may even needs a french drain.
Some pictures would sure be a big help both inside and out.
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Here are some quick pics. The outside pictured is a naturally watered garden and a lilac bush. Other side not pictured is just grass/dirt and the neighbors driveway. When we moved in, there was no elbow on the down spout and I added the tubing to take rain water away from the side of the house. The smell of damp concrete mostly went away after that. In the process of fixing the crack...