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DEPARTMENTS INSIDE CSI * HORIZONS * FAILURES FAILURES Terra Cotta: No Bad Repair Goes Unpunished Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at David S. Patterson, AIA, is an architect and senior principal with the Princeton, New Jersey, office of WJE, specializing in investigation and repair of the building envelope. He can be contacted at Jeffrey N. Sutterlin contributed to this article. The opinions expressed are based on the authors’ experiences and do not necessarily reflect those of CSI or The Construction Specifier. Terra cotta cladding exists on a wide range of 19 th and early 20 th century buildings throughout the United States, as well as on newer structures. The material can be very durable as a façade— most problems are related to deferred maintenance or inappropriate past repairs. Failure of terra cotta repairs often occurs because the work did not address the causes of distress (e.g. cosmetic fixes), or because the repair materials themselves were either not durable or incompatible with the existing original materials. In other cases, poor detailing or implementation is the culprit. Examples include: • surface-applying cementitious repair material over an existing crack, which does not prevent water infiltration into the crack or accommodate movement (where needed); • surface-applying sealant over a moving crack, which does not protect against water infiltration; • installing sealant in joints in the face of the wall, which (except at interfaces such as window perimeters, or at changes in façade plane) should be pointed so moisture can escape through the mortar—sealing these joints can trap moisture within the wall, leading to corrosion of embedded steel and cracking of the adjacent terra cotta; • using patch materials incompatible with the terra cotta substrate, or not properly detailed and anchored to backup, which leads to failure of the patch and, in many cases, of the adjacent original material; and • using replacement units, patches, or coatings that do not visually match the original material. Not only do inappropriate repairs themselves fail, but they can also lead to further distress and failure of the original terra cotta. A badly repaired crack can beget a more severe one, allowing more water to enter the masonry, accelerating corrosion of embedded steel, contributing to continued cracking and spalling, and creating an ongoing cycle of failure. Sealant was installed over the joint at the toe of the relieving angle (A). Cracks were repaired by surface application of mortar and sealant (B) and have re- cracked. These inappropriate repairs have led to continued cracking of the original terra cotta (C). Photos courtesy David S. Patterson and Jeffrey N. Sutterlin Sealant was installed over the joint at the toe of the relieving angle (A), trapping water in the wall and leading to cracking and spalling of the terra cotta. In response to this distress, non-matching, poorly executed, and un-anchored patches were installed, which have failed and become displaced outward (B). The original terra cotta unit adjacent to the patch has also become displaced; the displaced repairs and terra cotta unit present imminent hazards. To avoid failure, terra cotta repairs should: • address the cause of the observed distress; • employ materials compatible with the substrate; • be properly detailed and implemented; • not disrupt drainage patterns within the wall assembly or interfere with original system’s breathability; and • be durable, maintainable, and aesthetically appropriate. cs 98 the construction specifier | november 2013 CS_November2013.indd 98 2013-10-16 11:30 AM