In a storage area in my basement, the ceiling is not finished. I notice recently that the wood joists for the main floor are covered in these patches of black. Is this likely mold or something else (burned wood?). Is there anything to do or check, or should I just get a mold detection kit?

photo showing area of concern another area of concern yet another photo

The house is only a few years old. This is an unfinished storage area and it is not typically that moist in there. I put in some desiccants and they've barely absorbed any moisture, but I can't remember if the wood liked like this when I moved in. I don't really see anything on any of the exposed wall framing or OSB subfloor that looks like this in this unfinished area either.

  • 1
    that looks like writing
    – jsotola
    Commented Dec 31, 2021 at 0:09

2 Answers 2


The existing answer does a great job of telling you what it is but you should also know how to visually identify mold. Albeit, sending a sample to a lab is the only 100% way to be certain.

New mold starting

enter image description here

Ongoing mold

enter image description here

Dried and dead mold

enter image description here

Dry and fresh mold mixed

enter image description here

Mold rotting issue

The structural integrity has been compromised and the proper fix is replacement.

enter image description here


This looks like black spray paint. Mold would tend to have a less uniform appearance, and you would likely have other indications of moisture.

  • 3
    Absolutely correct. It's very common for truss plants and lumber yards to label orders after they're accumulated in a stack.
    – isherwood
    Commented Dec 30, 2021 at 19:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.