Tuckpointing is the process of repairing or refilling mortar joints in brick. The name comes from the action of tucking or packing mortar into the damaged joint with a tool called a tuck pointer. Mortar joints play a critical role in the structural integrity of a brick wall. They hold the bricks together, bear the compressive weight of the wall, and keep out water. The mortar is also the weak link in the brick wall system and is designed to deteriorate faster than the brick itself. Repairing mortar now may mean you won’t have to replace a damaged brick later.
Keep in mind that new mortar usually has a different coloring than old, weathered mortar, and it is difficult to blend the tuckpointed joints with the surrounding areas. You can help blend the colors by adding a cement dye to the mortar mix; this is particularly helpful if the old mortar has been dyed. Bring a sample of the old mortar to your masonry supplier for help with choosing a dye.
Source: The Spruce