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Question DetailsAsked on 9/24/2015

Mold smell coming from section of slate floor

We noticed a mold smell coming from our family room a couple months ago. We think the smell is coming from a small section of our floor that's next to our sliding glass door. We took up a large floor rug that was covering that area and the back side of the rug smelled really badly of mold. There was one heavy rain 10 months in which water backed up to the sliding glass door.

I had a mold inspection done and it really wasn't that helpful because indoor air tests didn't tell us how much mold we have or where. The inspector did notice roof leaks but it hasn't rained here in months so I cant image a new mold smell would come from a leaky roof when it hasn't rained in 9 months. Part of the problem is that it is a slate floor on a slab. The rest of the house is on a crawl space, but this room is not. I don't think there are any pipes running under the slab because it is an addition to the house. Also, the walls appear dry with thermal image camera and no visible signs of mold. Any ideas?

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1 Answer


Next time it rains, check that area closely - or if daring you could use a sprinkler to test it.

Obviously, if surface water is getting to that area - even up against the edge of the slab on grade, then you need to use surface slope, swales, guttering and downspouts, etc to direct water away from the house. Note thsat the water does not have to come above the slab to cause mold under rugs - just the natural moisture wicking and vapor diffusion through concrete can do that, especially with solid or rubber-backed rugs.

The other possibility is you have a door leak - either because of blockage of the drain channels in the metal sill plate, leaking door seals, lack of drip edge /drip edge sill plate overhang so the water running off the doors is wicking back under the door, etc. Lack of an overhang or awning or porch roof over sliding glass doors is a major contributor to this sort of problem.

Answered 5 years ago by LCD

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