Uneven Surface

Help! My house is 6 years old and the downstairs floors seem to have been coated with a black uneven substance that I presume is to keep out damp. How can I lay tiles on this surface? (I can't remove it).

Floor levelling compound ?

Can you nail things into the surface? If so then hardboard. Before going ahead, read up on it, there's a few rules to follow. Won't post them all unless it's actually a goer....

Surely ashfelt is normally black (but then thats usually level too), did see a guy at a new house build, painting the concrete floors black, but that was just stopping the dust.
Not sure about tiling with ceramics to be honest, re. what the recent gent was saying about laying wood over the concrete, so I would not know if that was correct or not......but I would be carefull about nailing into a concrete subfloor without checking for pipes first
As a carpet fitting company we do not even nail gripperrods down onto concrete floors, as we've put nails through pipes before now !