I'm installing some carpet tiles in a rented office. The previous tenant did me the favor of ripping up the existing carpet and pad, and there is a wood subfloor, but over that (under the carpet pad) was some sort of black stuff that looks like tar paper. I am not going to be able to get all of it off. It feels kind of dusty in places, and I'm concerned the carpet tiles won't stick to it well. I need some advice on how to proceed. I thought about pulling up as much of it as I can and then trying the tiles on top, or perhaps putting some sort of primer down over the black stuff. Thoughts?