What is this pattern on old wood in my old house?

Question

I live in an old house built in the 1950s. The basement is part unfinished and some of the ceiling boards have this weird black, spiderweb type pattern on it. What is this? Is it mold? If so are there any recommendations to remove this without damaging the wood that is ceiling joists in the home?

I've only been in the house for a few months. So I'm not sure how long it's been there. Basement does smell a bit musty. I do run a dehumidifier when it gets above 40% humidity now.

I've read vinegar can get rid of mold. Should I try some of that on the area?

Thanks for any input.

Answer 1

OP's solution posted as an edit to the question:

Here is what I ended up doing. Disclaimer I am definitely not an expert. I also had white spots that were likely mold. I did not notice/find any water leaks, the house is 70 years old. So I'm assuming some mold has just grown over time. I read bleach is not necessarily good for mold removal on wood. So I decided to try other chemicals. I've mixed 3% hydrogen peroxide (store bought) half and half with water in a spray bottle. Sprayed down, let sit for at least 10 min, scrubbed off (wearing p100 respirator, eye mask, and gloves), rinsed with water, and dried off. So far this looks to have effectively removed the mold and the patterns seen in the original image.

In terms of preventing, and getting some mold in difficult spots, I may try Concrobium to kill and prevent further growth. Alternatively, I also have basic Borax that I might mix into a solution and apply after my hydrogen peroxide to try to prevent further growth. Bora Care with Mold Care (which actually contains some of the same ingredient as Borax) sounds like a good product to apply too, but is quite expensive and might be overkill for my situation.

Answer 2

It is mold. I've had this exact pattern in a house I use to have in Texas. Just put some Clorox Bleach in a spray bottle and spray all of the floor joists and supports. (The little strips of wood between the joists.)

There is no need to wipe it down after. Just let it be.

You do need to make sure that your basement is ventilated though. The easiest way to check is to light several incent sticks and watch the smoke trails. (Make sure the door is closed as it normally would be.) If the smoke just rises, I'd recommend installing at least 1 electric vent. Mine had one, but it hadn't been cleaned in years.