We recently renovated a half exposed room in a 1960s split level. The floor is on a concrete slab with no crawl space underneath. Whenever it gets humid, there is a musty, cement like smell. My guess is that the slab is sweating. When we renovated, we chose a vinyl plank with an attached cork underlayment, and laid that directly on the slab. If I pulled the plank back up and added a vapor or thermal underlayment, would that help the situation? The flooring manufacturer recommended no more than 3mm. I’ve read a few articles that suggested xps board on top of slab to insulate, but I have two adjoining doors to this room so I can’t go too thick. Also, is there anything I could put on the concrete that could help, like a sealant?
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I'm not an expert, however, I'll share my own experience. I also live in a split-level house, and had the same issues as you, but, I had much more moisture problems. The drywall in the lower floor showed signs of water damage and mold from seepage. I wound up having a French drain installed just below the level of the footer just outside the the perimeter of the house. It was a black, corrugated, flexible plastic pipe with holes drilled in its periphery. As the ground water rises during heavy rains, it seeps into the ground and then into the block walls and slab, but with the French drain installed, the drain becomes the least path of resistance to the ground water flow, and it seeps into the drain instead of the walls and slab. I also regraded the soil around my house so that rain runoff flowed away from the house. I also had new gutters, downspouts, and cement troughs to direct the gutter water away from the house. The combination worked well for me.
Bigbro51
Thanks @bigbro51. We were contemplating doing the exterior drain tile/French drain too. Pricey, but it will save the house! Did you install the drain around the entire footer of the home or just the one room?