There was recently a leak in our shower on the main floor that was fixed when it was discovered, but it had to have been there for maybe a month. It wasn't a huge leak, and it ended up mostly draining into the basement below without running into too much along the way. I have no doubt some of it could have gotten into places for things to grow. The leak was fixed at least a month ago.

Just now I was in the basement and noticed what I think might be mold. It's in the general vicinity of the leak and you can see old water stains from what I would assume was that leak. This appears to be fairly isolated as I don't see anything similar to it or what other forms of mold look like. The best way to describe the substance is clumpy or sooty. I accidentally poked it and it fell apart like soot does. I haven't done anything with it yet, but I'm assuming it is mold. There also isn't any smell of mold down there or near it either.

Given the small quantity of it, would it be considered a DIY job, or should I call someone?

Side shot:

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  • There are two separate things in the picture. One is the oily substance on the beam at the top, and the other is the fluffy black stuff coming from the seam. – Steve Jul 29 '16 at 21:16
  • Can't see that from your straight-on photo. Maybe a side shot would help. It's possible that dissolved material re-crystalized in a "fuzzy" structure. If you crush it between your fingers what does it smell like? – isherwood Jul 29 '16 at 21:19
  • I added a side shot. Bit of a difficult angle to get. Does that help? I have yet to smell it for obvious reasons. – Steve Jul 29 '16 at 21:27
  • If it is mold, the problem is it also exists where you can't see it, or clean it. – Tyson Jul 29 '16 at 22:06

Doesn't look like mold to me but hard to be sure... If you're sure it's a small amount, and not the tip of the iceberg it's certainly DIY'able. Diluted bleach works well as a treatment. Wear a respirator, remove as much as you can and then spray liberally with diluted bleach. Ought to take care of it...

The way it's running out of the seam it looks more like mastic or something to me but I don't think a little bleach is going to hurt you either way for peace of mind.

  • There is tile above it so maybe. The house was built in 2002. I don't know if its still a common material for that? – Steve Jul 29 '16 at 21:19
  • Yeah... if there's a tile floor above, I call mastic. It just doesn't look like the typical black mold I've seen, and I've seen lotsssssssss of it – PaulBinCT2 Jul 29 '16 at 21:25
  • I added a different angled shot. Same opinion, or...? – Steve Jul 29 '16 at 21:27
  • Hmmm... are those stalactites? I'm going to stick (wink wink) with mastic. It's certainly odd but I've never seen mold grow that way and I've done years of remodeling, including lots of water damaged/rotted remediation. It may well be that the water dissolved something in the mastic that formed those deposits as it dripped and dried. In my experience, mold tends to stay in close contact with it's food source. If you are inclined and able to get a good macro photo I'm happy to look again but it just doesn't look like any mold I've ever seen. – PaulBinCT2 Jul 29 '16 at 21:38
  • Well hmm. I think you might be right. I'll give it a poke and try and collect some of it then spray it down with the bleach mix. – Steve Jul 29 '16 at 22:01

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