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Strange Black Substance in Concrete

longtee81 (Zone 5a)

7 years ago

I noticed for the first time (10-year hold home) that there were two areas in the basement (one towards the floor, the other towards the ceiling) that looked like a black substance that was hard, but crumbled into dust when I removed it.

I did paint it with a waterproofing substance (Behr) about 8 years ago and have had no issues (I know this is ill advised, but didn't know at the time), but I'm wondering what this could be and if it is something to be concerned about since I'm considering finishing it.

The paint chipped off around it. It's a poured concrete wall. I have never had any moisture issues yet.

Thanks!

Wall 1 (Pic 1) - Near Ceiling

Wall 1 (Pic 2)

Wall 2 - Near Floor

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Comments (3)

dgeist
7 years ago
Looks like some kind of contaminant in the surface (organic, maybe?). Were you able to get a little bit of it to take a look at under a magnifying glass, etc? It could have been there since the wall was poured and that part simply crumbled off because the paint didn't adhere to it properly.
longtee81 (Zone 5a)
Original Author
7 years ago
I didn't get a chance to view it under a microscopen bit removed it and it basically crumpled I would describe it as smelling like gun powered (carbon?). I'll try to upload some pictures of what it looks like after its removed. I cleaned off the spot with a wet paper towel and the black dust turned to towel black. It seemed to grow on the wall which is really strange to me! Not sure if it happened at once or over time, but we had just noticed it this year.

Thanks,

Steve
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dgeist
7 years ago
If it has a pattern (like a row or dots or a thin line) it might be the rusted tips of the old metal forms from when the wall was poured.

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