Diagnose brick spalling caused by a prior repointing job that used hard portland-cement mortar on soft historic brick

Steps

1. Inspect the failure pattern: spalling concentrated at brick faces immediately adjacent to unusually hard, dense, gray mortar joints (rather than uniform brick deterioration) is the classic signature of a mismatched hard-mortar repair
2. Scratch-test the suspect mortar joints versus the brick (a nail or knife) — mortar that is harder than the brick itself is a strong indicator of an inappropriate prior portland-cement repointing
3. Check whether spalling correlates spatially with a documented or visually obvious prior repointing campaign (different joint color/texture/profile than original areas)
4. Confirm the mechanism per NPS guidance: hard, low-permeability mortar forces moisture trapped in the wall to migrate out through the softer brick face instead of the joint, and freeze-thaw cycling then spalls the brick face
5. Specify remedial work that removes the offending hard mortar and repoints with a softer, more permeable lime-based mix appropriate to the original brick, rather than simply patching the spalled brick faces
6. Where spalling has progressed to structural section loss, plan for selective brick replacement (dutchman repair) in addition to remortaring, not remortaring alone