Why is mold/mildew growing behind my rigid foam?
So I had started to finish my basement area and read all of the articles on GBA. I was using 2” of XPS foam on the cinder block walls and recently had to remove a bunch to access an area for the egress window. When I pulled it off, I was surprised and scared to see that I had black stuff growing on the cinder block. I don’t know if it’s mold or mildew, but it can’t be good, right? You can even see how it’s growing around the foam adhesive that I used to attach it to the wall.
Not sure why this would be the case. I keep my basement at less than 50% RH and there is no issue with water. In fact, I’ve kept cardboard boxes on the slab floor for years without any issues.
What should I do? Thanks.
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