The main purpose of a chimney is to vent combustible products, such as the fumes from a gas fireplace, out of your home. Key to maintaining the integrity of your home’s chimney, repointing is simply a process that replaces the outer part of the mortar that holds the chimney’s bricks in place. Repointing focuses on the outer layer of mortar because that’s the part directly exposed to the rain and snow, which causes the mortar to crack.