From outside
- Recessed or missing mortar. NPS lists the usual signs as disintegrating mortar, cracks in mortar joints, loose bricks or stones, damp walls and damaged plasterwork. If you can see deep gaps between bricks, water can get in.
- Sandy or crumbly joints. Mortar that rubs away with a finger has lost its binder.
- Spalled brick. Faces popping off bricks are a sign of trapped water, and sometimes of mortar that is too hard.
- Stains and growth. Dark streaks below sills or gutters, and plants or vines rooted in joints. The Rowhouse Manual notes that vine roots can destroy mortar.
- Clogged weep holes. The Manual suggests clearing the small weep holes near the base of a brick wall so moisture can drain.
From inside
- Damp patches, peeling paint or plaster on the inside face of an exterior wall, especially after wind-driven rain
- Stains near window heads
Before you blame the mortar
NPS warns that it is “erroneous to assume that repointing alone will solve deficiencies that result from other problems,” such as leaking roofs or gutters, settlement or rising damp. Fix the cause first. The Rowhouse Manual’s maintenance checklist includes cleaning gutters, checking flashing, and watching for water staining on walls. A good contractor will look for the source, not just the symptom.
How urgent is it?
Failing joints let water in, and in freeze–thaw winters that damages the brick behind them. Loose bricks or masonry over the sidewalk are a safety issue; deal with those right away. Most other pointing can be planned for a season when wall temperatures are between 40°F and 95°F, the range NPS recommends.