POINTING
It is essential that the mortar used for repointing have similar performance characteristics to the original mortar used in a building. Such performance characteristics include permeability, compressive strength, and coefficient of thermal expansion. For instance, if a soft lime-based mortar was originally used, the most appropriate repointing mortar is likely to also contain a large amount of lime. The use of Portland cement mortar for repointing on older buildings with soft masonry units can cause significant damage due to physical incompatibilities.