also try using a metal bond diamond. the copper bond diamonds are aggressive and can do the trick
Hi Carl I would think sand paper open face type abrasive for removing the most stock but be careful you don’t make a dip in the patch 120 grit.
I am doing a large Terrazzo restoration with a lot of patch work 4"x4" 3" round holes etc. who has found the fastest/best way to take down/flatten the initial patch after it sets up.