I'm working on refinishing the floor in my downstairs bathroom. I've
ripped up the nasty rental-grade carpet (who carpets a BATHROOM?!) and
the even nastier vinyl tile that was underneath. What's left is rather
uneven concrete slab with the remains of the 'cutback' tile adhesive. I
want to apply a self-leveling underlayment, but I'm unsure what to do
about the remaining cutback adhesive. Do I need to remove it before
applying the underlayment? The guy at the home-improvement store said
no; several flooring experts on the intertubes say yes. I actually
ripped up the tile a LONG time ago, and the adhesive has long since lost
its 'stick'. It really looks like nothing more than black paint, and I
suspect it would be hell to remove it.

Opinions welcome.