Removing cement to make way for tile
We've decided to redo the tile around our fireplace. The original tile was a pain to remove. It was adhered to the sheetrock, which became a mess. I've replaced the sheetrock with plywood except around the very edges. I plan to lay a thin wood veneer over the entire surface to be tiled, but there is some kind of mortar that I'm having trouble removing. See attached picture. It is very hard and is not coming off with a chisel or prybar. The sheetrock comes apart instead. I'd like to find the right tool for this job. Any recommendations? Maybe some kind of grinder wheel attachment for a standard drill?