Found a weird patch of black mold behind a baseboard in a house I was finishing in Phoenix last month

I was trimming out a bedroom in a 1970s ranch house near Camelback Road and pulled off a baseboard that was loose. Behind it was this dark patch about 8 inches wide that looked like mold but felt dry and powdery to the touch. The homeowner said they never had a leak there, so I'm wondering if it's something from the old construction methods back then. Has anyone else run into dry black residue behind trim in older drywall jobs?

3 comments

3 Comments

robert6599d ago

Used to think any dark powdery stuff behind old trim was just dust or maybe some old glue. This changed my mind after I found the exact same thing in a 1968 house in Mesa last year. Pulled a baseboard and there was that same dry black patch, tested it and it was old asbestos mastic from the original drywall tape jobs. That dry powdery feel is a dead giveaway, it's not mold at all just really old construction adhesive breaking down.

lewis.mila9d ago

Dry powdery feel is a dead giveaway" is exactly right. My buddy found the same stuff in a house in Glendale and @robert659 your comment is what made him test it instead of just cleaning it up.

river9528d ago

Whoa wait, you're saying that dry powdery stuff could be old asbestos mastic? That's honestly kind of blowing my mind right now. I've definitely seen that same dry black residue behind trim before and I always just figured it was either a weird old glue or maybe just really old dust buildup. Now I'm thinking about all the times I probably just breathed that stuff in without a second thought, holy cow.