I have a butt-ugly fireplace surround of 4-5" granite veneer. It's 12' wide and is far too massive a job for me to pull it out. The scale of the stones are wrong for the room, and it has been re-grouted unbelievably poorly - so paint won't save it. I would like to trowel on tinted concrete (perhaps using a hopper). My concerns are around products and preparation/adhesion. Help!