4" Angle grinder, diamond blade...done
Thought about this a bit more: Likewise you can buy a masonry grinding wheel for the grinder that will allow you to hold it flat like you were buffing out a car but this will take much longer. Better to get the high spots with the diamond "dry blade" they are NOT the same as a wet blade. While working in the chamber if you have a shop vac putting the hose in the chamber will pull out much of the dust otherwise you will not be able to see your work. This is not a substitute for a dust mask and good tight fitting goggles. Goggles are better choice for this situation because the dust gets behind the glasses, into your eyes and you will not be able to see. Its gets everywhere. When we do enclosed grinding we have an attachment for the shop vac that attaches to the grinder. When this is not possible to use a helper holds the hose right by the blade this eliminates almost all the dust and you can see your work as well as eliminates the need to bid a maid service to come in and dust the customers house ofter the job..
