Getting closer to the finish line on this project at Park Hill South High School in Riverside, MO! Below grade waterproofing, air barrier, caulking, and expansion joints were the scopes GKW handled on this project. Should be ready to go for the students to enjoy next school year.

Rethinking Masonry Cleaning as a Chemical and Thermodynamic Problem

The act of cleaning historic masonry is not a visual intervention — it is a chemical, mineralogical, and thermodynamic exchange.

Every substrate presents a different interaction with moisture, pH, and thermal loading. Brick, for instance, may contain residual salts that mobilize under saturation, leading to subfluorescence and irreversible spalling. Limestone, largely composed of calcite, reacts readily with acids, risking surface etching or structural degradation. Even water, if misapplied, becomes a solvent that migrates through capillaries, altering surface tension and redistributing contaminants beneath the surface.

Cleaning, in this context, becomes a study in phase behavior, porosity, and crystallization pressures. The failure to recognize it as such can introduce new pathologies into otherwise stable walls. The challenge lies not in removal, but in preservation of equilibrium—between the original materials and their environment.

In a field dominated by aesthetics, the most critical cleaning decisions are often invisible.

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Mortar Joints as Capillary Breaks and Mechanical Buffers

Mortar is not filler — it is a hygric, thermal, and mechanical buffer system engineered to absorb movement, regulate moisture, and dissipate stress within a masonry assembly.

The functional performance of mortar lies in its role as the sacrificial element—the part designed to fail first, to protect adjacent masonry units. That sacrificial nature is only preserved when mortar strength, porosity, and permeability are correctly proportioned relative to the masonry itself. Too strong, and the mortar induces stress; too impermeable, and it traps water behind the wall.

Over time, weathering degrades this function. Repointing, then, is not about surface repair — it is the re-establishment of the wall’s original performance logic. Capillary breaks are reactivated. Hygrothermal cycles are stabilized. Movement accommodation is restored.

The history of failed facades is, more often than not, a history of incompatible mortars.

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