Built in 1924, the Wrigley Building is one of the most recognizable landmarks in the United States. As the “jewel” of the Magnificent Mile in downtown Chicago, this national treasure requires careful maintenance and upkeep. Two key parts of this process are the annual visual inspections, required by the city once a year, and the critical inspection, which is required every 3 or 4 years. The latter of these inspections includes the use of suspended platforms to carefully inspect and test the exterior façade. Known for their expertise in nondestructive evaluation, CTLGroup was retained to perform the critical inspection.
The objective of the project was to determine the condition of the Wrigley Building’s exterior cladding, which is composed of precast terracotta panels. The CTLGroup team used Impulse Response (a type of nondestructive testing), standard sounding techniques and visual observation for the evaluation. The most common form of distress in terracotta, is the wearing down of the water protective coating. This allows water to leach through the outer shell, which can cause a breakdown of the grout filler material within the cladding. Due to the severe changes in weather conditions in the Chicagoland area, this causes a freeze-thaw effect, which breaks down the grout filler and causes debonding. Debonding can cause failure of the panels in the form of severe cracking to the outer shell or corrosion of the steel pins that attach the terracotta to the building. The latter can potentially cause the panels to fall off the side of the building.
CTLGroup delivered the results of the testing and made repair recommendations to prevent failures in the building’s historic cladding.