The chimney in the photos above has mortar joints that are soft enough that a grinder with a diamond blade can easily grind the mortar out. Good, solid mortar would cause the grinder to bounce off of the mortar joint when attempting to grind out the mortar.

(New mortar being installed past the edge of the bricks.)

When I come across a chimney with recessed joints that are in the early softening stage (if the softening has gone on for too long, the chimney should be rebuilt) , I recommend that the joints be ground out, then tuck-pointed with type N mortar. The new mortar would come all the way out to the edge of the bricks, thus eradicating the recessions, thus getting rid of the problem of pooling water. The mortar joints are struck to a concave finish:

New mortar joints, concave strike finish, no recessions for water to pool on.

Finally, we come back after 30 days of mortar cure time and apply a 10-year siloxane-based waterproofing agent to protect against frost wedging.

If you want to see a video of me demonstrating the tuckpointing procedure, then go here (9 minute video.)

Cliff Brand- owner

Rooftop Chimney / Willamette Chimney / Yamhill County Chimney

Oregon CCB # 193902. Licensed, bonded, insured.