Restoring Unity to Frank Lloyd Wright’s Reinforced-Concrete Temple

Unity Temple was conceived by Frank Lloyd Wright and constructed in Oak Park, Illinois in 1908-09. It was masterfully rendered, inside and out, in reinforced concrete. Unity Temple is an early example of Wright's use of concrete; both as structural and architectural elements.

CTLGroup's role comprised a survey and evaluation of the concrete's condition and the development of a phased rehabilitation plan. CTLGroup was required to achieve the highest possible aesthetic standards, maintain strict historical accuracy and protect the integrity of existing building features. Our engineers and consultants were charged to carry out repairs without interrupting the operations of the Unitarian Universalist congregation.

CTLGroup's restoration program succeeded in restoring the distressed concrete elements of this historic treasure. The Unity Temple Restoration Foundation derived the greatest benefit from their available funding.

Historical Documentation: Three varieties of concrete were named in Wright's original specifications: Portland cement facing mortar, stone concrete and structural cinder concrete (floor and cantilevered slabs). Each variety was confirmed and characterized from core samples taken and studied in the CTLGroup laboratories.

Condition Survey: CTLGroup engineers and specialists conducted a condition survey including: visual inspection, mechanical sounding, non-destructive testing and evaluation of core samples. All informed the restoration plan.

Documentation: Undersides of cantilever and fascia displayed cracking, de-lamination and spalling that posed a threat to the historic building, and, most immediately, to public safety. There was corrosion evident on one of the ornamental columns. The roofs deflected as much as 5 inches, exposing rebar to weather distress. Cinder aggregates contained iron particles that corroded, causing chunks of concrete to pop off the building.

Demolition: Conventional demolition methods were unsuitable because of their percussive, corrosive or water consequences. CTLGroup tested and recommended the use of an expanding chemical compound. When strategically injected into a series of sawcuts and drill holes, CTLGroup predicted and verified a controlled cracking-off of the defective concrete. By predictably breaking down the size of the pieces in this manner, the safety of adjacent art-glass windows, integrity of the façade and the protection of ornamental columns could reliably be addressed.

Fascia and Soffit Restoration: After demolition, fascias and soffits were newly reinforced and reconstructed. CTLGroup designed reinforcing concrete material to control shrinkage-related cracking in the future.

Ornamental Column Damage Mitigation: CTLGroup injected lithium hydroxide under low pressure, thereby increasing pH to lessen future corrosion.

Mix Designs and Acceptance: CTLGroup designed cementitious materials that would visually match that which was original. Trial mixes and field mockups were presented. Research led to sources of pea gravel and aggregate similar to that used in the original mix designs. Materials were purchased for the whole project to eliminating "batch" inconsistencies throughout the project.