When installing Ceramic Tile or wood floors you always want your substraight to be level and without bumps.
Although Mortar and Mastic will provide you with a little bit of leeway it is best to remove any high spots with a hand or electric grinder.
The choices you have in tools include a hand grinder like we will be using or electric models either a hand held disk grinder or a floor model for heavy jobs.
You should start in one corner of your room working the length of the room in widths short enough that you won’t miss a spot.
The top layer of Concrete is mostly Cement but if you hit a stone you have the choice of chipping it out or leaving it.
If the imperfections are lower then the height of the mortar and will leave room for good adheasion then you should leave the hardspots.
If they can be removed easily then you should try to remove the imperfections because they will cause trouble when you are spreading mortar.
A sponge and a bucket of water will aid in cleaning the grinding stone and will cut down on dust.
Remember to wear a dust mask and open a window for ventilation.
It is good to walk the room a few times to make sure you have removed all the imperfections and high spots.