The process of replacing the mortar is called repointing. To repair cracked or crumbling mortar, start by chipping out the old mortar with a chisel, wearing goggles to protect your eyes from flying chips. You’ll also need mortar and a small trowel.

You should match the finish of the mortar joints to match the existing joints so that you don’t introduce new points of wear. It will be difficult to get the mortar to extrude but other jointing types should be possible, such as finishing the mortar flush with the brick, making a V-joint or a concave joint. Cut off any excess mortar by sliding the trowel along the wall. Brush excess mortar off the wall and keep it damp for 3 or 4 days to cure.