How to level concrete floor that is chipped and has left over thinset
A silicon carbide grinding block (gray block with grooves, red handle, is the form I usually see - about 5x9x2 inches to start with, thinner as you use it and it wears down) is how you knock down the high spots.



After you do that you can use some type of levelling compound for the low areas - normal cement won't be happy in such a thin layer.