We just bought a house that was built in the early 50's and want to redo the floors and were thinking of a polished concrete look. Upon removing the current tiles, which are ceramic (I think they're 18x18), I noticed that there is black residue on the concrete. There was no vinyl tile under what I removed but I'm worried that what i'm looking at could be asbestos. I did order a test kit just to be sure but my question is if anybody experienced a similar situation with black residue under newer ceramic tile?

As you can see from one of the pictures, some of the black residue is stuck on the tiles. I'm hoping it's unlikely that any old mastic would adhere to this new tile I'm removing?

Any thoughts while we get the test results are appreciated!