I've appreciated the help that I've received before in these forums and so I'm back again.
There is a coating on our concrete kitchen floor (see pictures). It's black, thin (like paint), tarrish, but not sticky to the touch. I believe it has been on this concrete for a very, very long time (~30 years, I'd wager).
1) Is it absolutely necessary to remove this in order to obtain good bonds using thinset mortar?
2) It is gumming up my sandpaper very quickly - is there a better way to remove it?
3) If blasting is the only way to remove it, will this make a mess of our new cabinets?