Frank Lloyd Wright’s 1905 design for Unity Temple represented a significant departure from traditional religious architecture. The building’s façade of exposed, poured-in-place concrete, used at that time primarily for industrial structures, established Unity Temple as an early experiment and masterpiece of modern architecture.

As an experiment with new materials and unprecedented design elements, structural problems, including problems with Unity Temple’s concrete walls, appeared almost immediately. Wright accommodated the exterior geometric design, with 16 separate flat roofs, by creating an internal drainage system with downspouts concealed within interior columns. The system is ingenious, but inadequate and inaccessible. Unity Temple was well maintained, but years of hidden water infiltration caused extensive damage to the concrete structure. Additionally, because Wright’s experimental concrete design did not include expansion joints, there was extensive surface cracking.

By 1973 the original concrete was in poor condition. The decision was made to repair the concrete surface by applying a layer of shotcrete – pneumatically applied concrete – known as “Gunite.” The Gunite closely matched the original material, was composed of aggregate mined from the same source in Indiana as the aggregate used in the original construction. The application of shotcrete, at the time a radical intervention, likely saved the building. Since then, there has been additional deterioration of the concrete resulting in spalls, cracks, and corrosion.

Over the past fifteen years, Unity Temple Restoration Foundation has allocated significant resources to determine and implement proper repair and restoration techniques for the exterior concrete. All the cantilevered roof overhangs, for example, were restored in 2002. Project planning conducted in 2014 included extensive testing of proposed treatments to restore the exterior applied concrete.

The restoration project repaired and/or replaced the existing shotcrete in damaged areas. It is critical to select the cement, sand, and coarse aggregates to achieve a close match in coloration and texture to the existing shotcrete, allowing new areas to seamlessly blend into the 1973 surface. Tests conducted experimented with the proper mix of aggregate for the shotcrete, and utilized a range of finishing techniques to blend new with existing surfaces.

The restoration process included developing routine maintenance procedures to monitor the concrete for cracks and deterioration in the future, as well as an appropriate repair process to prevent water from penetrating the surface and causing new damage.