We are replacing hardwood floor that was glued directly to the slab. We have removed hardwood and are dealing with glue residue on the slab. It is wavy where the glue flowed into the texture of the wood.
What is the best way to remove the glue residue? I am using a pneumatic chipping hammer and it is incredibly slow.
How clean does the slab need to be before I put down the thinset?
Removing glue from a concrete slab is one of the most difficult projects imaginable. You can rent a floor grinder that will grind off the glue surfaces, but short of that, any kind of glue solvent or mechanical chipping is bound to be a slow and painful process.
Since you mentioned thinset, it sounds like you're planning to add tile. I would encourage you to instead consider laminate flooring vs. ceramic tile, which can look like tile or even hardwood and can float over the slab without being glued.
Laminate can solve both your problems at the same time. You install it with a thin layer of insulation - typically about 1/8" of foam. Sometimes it's attached to the back of the laminate, and sometimes it's a roll you roll out. The insulation goes between the slab and the laminate, so you've got some give.