I would not use any solvents, they would only create
a residue that may react wrongly with the thinset.
Just use a razor blade scraper and get all possible
loose material off, then using a high quality
multi-purpose thinset, skimcoat the entire slab
with a flat trowel...a very thin coat that you press
into the floor as you trowel it on. Let that thin coat
dry 24 hours and you'll have a great floor to bond to
with the same high quality thinset.
You can identify quality thinset not only by the higher
price (usually $15 and up a bag), but the small print
on the back of the bag will say that it will adhere to
vinyl, existing ceramic tile, exterior grade plywood
When I skimcoat questionable surfaces I use a
liquid additive made by Laticrete called "333".
Mixed with regular (NOT multi-purpose) thinset,
it makes a super strong coating, and an excellent
Have fun. How were you planning on making the
transition from slab to wood flooring area? Those
two surfaces will surely settle and move separately.
Many grout manufacturers make a sanded caulking
that matches their grout colors. I would caulk the
joint at this transition with sanded caulking. It shrinks
alot when filling a large gap (1/4" typical joint), so you
may need to apply it again after the first application