Water expands roughly nine percent when it freezes, and it does not negotiate. A hairline crack in a mortar joint takes on water in a January rain; that night the temperature drops, the water freezes, and the crack is levered a little wider. The next rain reaches a little deeper. East Tennessee does not have brutal winters — it has oscillating ones, which for masonry is worse: the freeze-thaw cycle runs dozens of times a season.
This is why old brick walls fail from the joints outward. The brick itself is usually fine; the mortar between courses is the sacrificial material, and once it starts shedding, the wall's water protection is gone and the process accelerates.
Repointing is the repair: grinding out the failed mortar to sound depth and packing fresh mortar in. Done before water reaches the wall's core, it is maintenance; done years late, it becomes rebuilding. The same logic covers stone veneer and block — anywhere mortar faces the weather.
Caps and copings matter for the same reason. The top of a wall, a column or a chimney is where water enters first, and a sound cap sheds it before the joints ever see it.
Brick work — new walls, steps and columns, and repointing of weathered joints — is one of the ten services at Garcia's Hardscape, alongside block and natural stone. Call (865) 314-3287; hours are Monday–Saturday, 8:00 AM – 7:00 PM.