Is this black stuff mold on the concrete foundation? enter image description here In the process of replacing the bath/shower plumbing and fixtures I started chasing mold from the surround. As I followed the trail underneath the laminate floor, I saw all this blackness. It was very damp under the floorboards, and I know I had mold in the bathroom. Just wondering if it might be some sort of concrete sealer or pre-floor coating or glue from a previous flooring. Hoping it's not all mold...

Thoughts? Thanks!

  • It is almost impossible to tell from a picture. Best thing to do, is have it tested and know exactly what you are dealing with. Some mold be told to just clean it, others be told to get out now. Might also just be paint/glue. Middle of picture on left hand side, looks like some of the black stuff is peeling, usually mold doesn't peel like paint. Testing is only way to be sure.
    – crip659
    May 15 at 20:49
  • 1
    Looks like mastic/adhesive for a tile floor. I suppose those look like trowel marks and maybe some marks someone made trying to scrape it up that are visible in the photo ?
    – gnicko
    May 15 at 23:18

1 Answer 1


There's no way to tell just by looking at a photo.

If it's mold. bleach will kill it and turn it white/colourless, If it's adhesive it will likely be unaffected by bleach.

we also can't tell if it contains asbestos, or lead, etc... by looking at a photo.

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