Summary: I would like to insulate the upper half of our basement walls with rigid foam. I know that our basement walls show some signs of excess moisture, but I'm unclear on the sources of that moisture, whether it is an ongoing concern, and what would constitute "good enough" remediation (good enough to install the rigid foam as described).
Details: We're in Massachusetts in a 1930 house, the soil in our area is classified as "fine sandy loam". We have gutters on all sides with downspouts that are extended a couple of feet away from the house. They're cleaned regularly. The surrounding landscape is reasonably well graded away from the house. The basement walls are built from cinder block units and there is a concrete slab. At some point they must have been painted by an old version of drylock-type paint.
Symptoms: About 50% of the wall area looks ok, with only some chipping paint . There is some minor spalling in the bottom two rows of concrete blocks in about 40% of the walls . One wall area, about 10%, has more significant spalling up to about the 7th out of 10 rows of concrete blocks.
I have to run a small dehumidifier to keep down relative humidity. I have used the “plastic sheet test” (taped a small piece of foil to the wall and checked for wetness on inside and outside surfaces), which came out dry on both sides.
I’m assuming that the spalling in the bottom rows is a kind of “rising damp” from below. Given the age of the house, I guess there is not much in terms of a capillary break. Confusingly, the area with the more significant spalling higher up on the wall actually abuts our mudroom, which has a vented crawl space on a dirt floor. I would have assumed that this would keep the foundation dry, since there is no way for rain to fall right next to that wall.
Proposed solutions: I’m not sure what else I can do on the exterior to reduce the moisture in the wall. My plan right now is to clean and patch the spalling concrete and then use drylock or a similar product. After this, I will glue rigid foam to the upper half of the wall, to only cover the above-grade portion of the concrete and the top 2’ of below-grade area. My hope is that this will allow the wall to dry in the “wetter” bottom rows.
Questions: Will the proposed solution keep the walls dry enough to install rigid foam? How will I know that I have succeeded in managing the moisture?