Repointing

Repointing is the process of grinding or chiseling out deteriorated mortar from between bricks or stones, usually to a depth of about half an inch to three-quarters of an inch, and packing new mortar into the cleaned-out joint. It's a structural repair, not a cosmetic one: it's done when the original mortar has eroded, cracked, or crumbled enough that the wall is losing the protection and load distribution the joint is supposed to provide. The new mortar has to match the type and hardness of the surrounding original mortar.

Freeze-thaw winters erode mortar joints faster than they wear down the brick or stone itself, so repointing on a reasonable schedule is one of the most effective ways to protect masonry up here before real damage starts. It also has to be done right: cutting joints too deep, using a mortar that's harder than the original, or grinding into the brick edges instead of just the joint can do more harm than the deteriorated mortar was doing on its own.