What is chimney repointing, and does it stop leaks?

How repointing is done

1. The mason removes damaged mortar to a depth of roughly two to two and a half times the joint's width, without chipping the brick edges.
2. The joints are cleaned and dampened.
3. New mortar, matched in strength and color to the original, is packed in layers.
4. The joints are tooled so they shed water.

Mortar that is harder than the brick, a common mistake in amateur repairs on older chimneys, can make the brick itself crack and spall, so the mix matters.

Signs a chimney needs it

• Mortar that is recessed, crumbling, sandy or missing.
• Bricks that wiggle.
• White mineral deposits on the brick, showing water moving through it.
• Damp walls beside the chimney indoors after long rains.

Repointing and roof flashing

Counterflashing is set into mortar joints, so eroded joints at the roof line can let water behind the flashing even when the metal is fine. The best order is repointing above the roof first, then reflashing with counterflashing cut into the fresh joints. Some masons also apply a breathable water repellent after repointing; avoid sealers that trap moisture in the brick.

Who does what

Repointing is masonry work, while step flashing, counterflashing and crickets are roofing work. A leak beside a chimney is more often flashing than mortar, so confirm the source before paying for either. See chimney leaks and crickets and roof flashing explained.