Cleaning concrete floors?

Question

I recently pulled up some tile in my bedroom to reveal the concrete floor underneath. The problem is, there is a layer of black stuff that we assume was glue, but we aren't really sure. It is next to impossible to get this floor clean. You wipe and wipe and wipe, and it's still dirty.

So, the point is...

Anyone have any ideas for removing the black layer and getting the floor clean. I'm hoping to paint it soon.

Answer 1

doesn't it absorb the water?

you have to scrape it off

Answer 2

Try CLR Degreaser it wored on our garage floor really well.