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Mortar Analysis
by Tomasz Glab There are many decisions facing anyone who is initiating a masonry restoration project — and selecting the appropriate restoration mortar for repointing or spot-pointing historic masonry can be particularly challenging.
If the newly installed mortar is incompatible with the original building design, the building may develop a range of problems, including spalled and cracked masonry units and elevated moisture in the wall systems. According to National Park Service’s Preservation Brief 2: “Repointing Mortar Joints in Historic Masonry Buildings,” restoration mortar formulation must be as vapor-permeable and as soft as or softer than the historic mortar (measured in compressive strength). The new mix should also have greater vapor permeability and be softer than the masonry units. The sand should match the original as much as possible in color and texture.
In addition to compatible performance, the appearance of newly installed material should also be consistent with the original. The best way to select an aesthetically appropriate, high-performing restoration mortar is to first understand what was originally installed in the building.
Mortar analysis, including testing, is often an essential step in a successful mortar restoration project.
