I am repointing a building that uses 6-inch-thick granite blocks as an integral part of the exterior masonry walls. What mortar is appropriate for the granite?
Typically, the repointing mortar should match that used in the wall originally. The general rule is that the repointing should be the same strength or weaker than the original mortar to avoid stress concentrations. In newer stone masonry walls, Type N mortar should work well. I would follow the recommendations for brick masonry, including wetting the joints before applying mortar and installing prehydrated mortar in 1/4-inch-thick layers.