- Whenever mortar has lost 1/4 inch of its original depth, it's time to get out the chisel and go to work. Thoroughly rake out and clean joints to a depth twice the width of the joint.
- Do not chip, cut or remove the brick's fire-skin, which will accelerate decay.
- Make sure the brick is stronger than the mortar. In general, houses built before 1930 have softer brick, which makes them likely candidates for old-style lime mortars. To know for sure, have an engineering lab analyze a brick for compressive strength.
- Repoint only when temperatures remain between 40 and 90 degrees Fahrenheit, even at night. Cold makes mortar brittle, while heat dries it out and prevents hardening.
- Keep fresh lime mortar damp for at least 3 days so it can harden before it dries. Taping plastic sheets over repointed areas will slow evaporation. After the sheets are removed, hose the wall periodically during dry spells to speed hardening.