DavidM47 t1_j5t6jwu wrote on January 25, 2023 at 11:48 AM

OP, I was going to say that I don’t think it’s mold, because I don’t think mold can grow on concrete, but apparently it can! And it does kinda look like that when it does. Search for leaks. Check to see if you have a dead valley at your chimney. If so, you need to install cricket flashing.

OzAnonn OP t1_j5t9p2s wrote on January 25, 2023 at 12:22 PM

It used to have a leak, not sure for how long as I bought the place last year. The crown was leaking. The flashing was okay.

DavidM47 t1_j5t9u0r wrote on January 25, 2023 at 12:23 PM

The discoloration may be permanent even if spores are gone

OzAnonn OP t1_j5ta0n8 wrote on January 25, 2023 at 12:25 PM

I don't really care about that. More of a health concern

OzAnonn OP t1_j5t9w6g wrote on January 25, 2023 at 12:24 PM

Wouldn't mold smell? I have a very strong sense of smell but there's no musty smell around this.

DavidM47 t1_j5vcl1m wrote on January 25, 2023 at 8:43 PM

There are many different types of mold. But I think for most of them, the smell (and definitely the biohazard) comes from the byproducts not the spores. So the smell could be gone but the discoloration remains.