In prepping my basement floor for tile, I started tearing out the carpet and found spots of black mastic patches stuck to the concrete pad. I had them tested to contain 4% asbestos. So my question is, are these patches of black mastic in themselves dangerous? Or only if I start sanding or breaking them apart? I feel like I should just leave them alone and go right over them, but they are exposed at the moment so I'm a bit worried about them.
Not a tile guy, they will have to tell you if you can go over it. If you can leave it, thats what you should do. If you scrape it up, just keep it misted with water and wear a mask. It is not dangerous unless it becomes friable.
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Installing since 1973
Just sitting there won't harm anything. If you do anything with it just do like the above poster already said. Your bond to the floor is only as good as what you go over. If it is dried out or flaky the possibility of bond failure of your tile is increased. I personally would get rid of it.