Stone in Philadelphia
Wissahickon schist, a silver to brown mica schist, is quarried locally as a building stone. Mount Airy is known for large gray-stone houses. Many rowhouses also have brownstone at the base of the facade and around doors and windows, according to the Rowhouse Manual.
Pointing stone
The same principle applies as with brick: NPS Preservation Brief 2 says the mortar should be softer and more permeable than the masonry units. Stone joints are often wider and less regular than brick joints, and the mortar color and texture are a big part of how the wall looks. Ask for a sample area first.
Brownstone
The Rowhouse Manual says deteriorated brownstone “should be replaced with matching stone, not patched or covered with stucco.” Brownstone that is laid the way it came out of the ground, in horizontal layers, lasts best. Brownstone repair is specialist work, so ask contractors for examples of past jobs.
Foundations and basement walls
Inside a basement, loose or sandy mortar in a stone or brick foundation wall is common in old houses. Repointing it can help, but water coming through the wall usually has an outside cause, such as grading, gutters or a leak, that should be fixed first.
Costs and permits
National cost surveys price pointing by area; see the cost guide. Pointing usually needs no building permit unless the property is on the historic register. Several Northwest Philadelphia areas have local historic districts, including Germantown Urban Village and the Central Mount Airy commercial district.