Our project posts often include photos of our staff matching new brick to that of the existing building. But we also pay close attention to the mortar that holds the masonry units in place, resisting movement and water infiltration.

There are five basic mortar mix varieties: M, S, N, O, and K. For fans of mnemonic devices, those letters are derived from the word MASONWORK. Mixes vary according to their ratios of cement, lime, and fine aggregate (sand).

Mortar selection is not just a matter of matching color and texture. Specifying the proper mix is crucial. The difference of one letter can make or break a project.

After a large facade repointing project for a major agency (performed by another consultant), significant water infiltration persisted. SUPERSTRUCTURES was called in to study and remediate the issue.

The previous consultant had specified repointing of all brick mortar joints using type O mortar—a mix not generally recommended for exterior applications because of its porosity. We specified petrographic analysis and Rilem tube testing that confirmed that the type O mortar was admitting water into the brick wall at a rapid rate.

The remedy suggested by SUPERSTRUCTURES, subject to field verification, was replacement of the Type O mortar with Type N (which in any case is a more conventional choice for exterior applications).

Indeed, subsequent performance testing of in situ mockups repointed using type N mortar exhibited a substantially reduced rate of water absorption. Once repointing of the entire facade is complete, the building envelope is expected to be safe and watertight for years to come.