Follow NPS Preservation Brief 2 workflow for repointing mortar joints in historic masonry

Steps

1. Determine repointing is actually needed (deteriorated/missing mortar, cracking, water infiltration) rather than a purely cosmetic wash, per Preservation Brief 2's framing of the mortar joint as the wall's first line of defense.
2. Analyze unweathered historic mortar samples from protected areas (under sills, behind downspouts) to characterize binder, aggregate, color, and joint profile before specifying a replacement mix.
3. Remove deteriorated mortar by hand-raking to a joint depth of roughly twice the joint width (or to sound mortar), avoiding power grinders that widen or damage masonry unit edges.
4. Thoroughly wet the raked joints and pack new mortar in thin layers, letting each layer become thumb-print hard before adding the next.
5. Match the original joint profile (e.g., struck, weathered, flush) when tooling, since profile affects both appearance and water shedding.
6. Cure new mortar under damp burlap or misting for several days, protecting it from rapid drying, frost, and direct sun.