I know I should not worry now but back in 2019 when having a shower, part of the shower handle fell. It is evident that the tiles themselves were full of mold ....But what about the black thing that got exposed once the handle fell off? I tried to bleach it and it would not come off.....So you think this could be mastic with asbestos? The house was built in 1930's. Please, help me figure this out! Thank you