Faux joints for faux stones Joints are scored with a speed square. Here, the square is held on edge to leave a rough, mortar like joint. The square is held flat for a smooth joint. Also the speed square marks off a dark line accenting the joint. On these faux granite blocks, the brown coat was scored first creating a deep joint. The finish is scored with a cheap concrete groover, making a nice dark joint. Joints are made on this faux brownstone water table sill by taping the brown coat, and pulling off the tape when the mortar sets up.. Faux limestone joints are made using 1/4" masking tape. This tape is available at an automotive paint supply.