Close up of possible moldChunks with black moldhole clean of debrisWe have only been in our home for 4 months. Built 1970. I'm getting ready to skim coat the walls of the living room. I'm prepping the surface and I had a spot where the drywall got knocked off when removing the baseboards. I'm vacuuming and picking away the excess when I notice there's black mold on the paper facing the inside of the wall...

How concerned should I be about this? Other side of this wall is just the exterior. Nothing seems moist. The wood I can see seems old but not rotted. There is a rectangular patch further up the wall where I'm guessing a wall AC unit may have been. I'm assuming this is from an old leak and it hasn't really spread. I have a humidity monitor and our indoor humidity is good at 37 percent.

I found one other small bit of mold on another area of baseboard across the room. I cleaned it with bleach and then sanded the area a few days later and no sign of further penetration of the mold in that spot.

Would painting this section of wall with KILZ original be sufficient or do I need to do some more digging to see how extensive this is. And if so, how do I go about patching it up?

  • Are you sure it is mold, or just black tar paper used for insulation
    – Traveler
    Commented May 1 at 1:52
  • @Traveler Ah, great point. I'm not familiar with it.
    – Alex
    Commented May 1 at 2:09
  • If bleach kills it it is mold
    – Traveler
    Commented May 1 at 2:11
  • the first picture looks like tar paper
    – jsotola
    Commented May 1 at 5:27
  • That looks like mold and roach droppings. The pictures indicate that there was /is some water infiltration inside the wall.
    – RMDman
    Commented May 1 at 12:33


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