By: Andrew Houston
Like all exterior building materials used in a cold-weather climate, terra cotta segments are susceptible to the aging and weathering process. The annual freeze/thaw cycle is almost certainly the most damaging over time. When temperatures are below freezing, moisture within the terra cotta expands and can cause crazing, large cracking, or even spalling.
Any building with a significant amount of terra cotta comprising the façades should have a regularly scheduled maintenance plan in place. The terra cotta should be regularly cleaned and a full closeup visual inspection and sounding out of the terra cotta should be performed annually. At a minimum, potential sources of water infiltration should be identified, evaluated and prioritized, to address deficiencies that can undermine a watertight façade.
Most manufacturers design glazed terra cotta segments to be easily cleaned using a simple mix of water and over the counter detergent, and a natural or nylon bristle brush for gentle scrubbing. However, building owners should attempt to locate original building documentation to be sure there are no particular requirements unique to their façade. The more difficult aspect of repair and maintenance is actually gaining access to the terra cotta, whether via suspended scaffolding, supported scaffolding, or some other method. Sandblasting or any high-pressure cleaning should be avoided, as this can cause permanent damage to the glaze finish.
Once the terra cotta segments are accessed, they should be visually inspected for smaller surface deterioration such as crazing, salt deposits, and chipping. They should also be assessed for more significant cracking, as well as to ensure that they have not rotated, become loose, or otherwise lost some connection to the original embedded anchoring system. All surrounding mortar joints should also be inspected. Once the visual inspection is completed, the surfaces should be sounded out; a rubber mallet or a small metal hammer can be used for sounding. A trained ear can determine internal cracks and failure that is not yet visual on the surface by the way the hammer “rings” when striking the surface of the terra cotta. Any cracks visible on the surface indicate previous failure, while a continuous crack that runs through several adjacent segments is more likely to indicate highly corroded embedded steel behind the terra cotta segments.
The required involvement and cost of these repairs can vary depending on the severity of the damage to the terra cotta. Waterproofing sealants and applications can be applied directly over terra cotta segments to prevent further water infiltration; however, installers must make sure that when applying a waterproofing layer, water is not trapped behind the material. This can actually do more harm than good to the overall building envelope. These waterproofing materials, especially cementitious coatings, can become de-bonded within a few years. Additionally, it can be very difficult to visually match waterproofing applications to the surrounding area, resulting in unattractive “blemishes” along an otherwise aesthetically uniform façade. Many building owners don’t realize that paying careful attention to mortar joints and ensuring their proper maintenance and protection is often the best way to increase the lifespan of a terra cotta façade. Open or otherwise defective mortar joints make up the majority of entry points for water infiltration.
At a minimum, more significant issues, such as cracks and spalls, will require patching with a repair mortar designed specifically for terra cotta. These deleterious conditions may also require the full removal and replacement of the terra cotta segments themselves, and/or steel repairs. Water infiltration can cause significant corrosion of the embedded anchoring steel, which creates pressure on the terra cotta. Over time, this pressure forces the terra cotta to crack, spall, loosen, or even fall off a facade.
Once a repair program is in place that requires the removal and replacement of full terra cotta segments, architects and engineers must fully understand the detailing of the anchoring system. Poor detailing of the new system can account for damage to the terra cotta segments much more quickly than the actual failure of the terra cotta.
With a clearly outlined maintenance schedule established, building owners fortunate enough to have terra cotta façades can rest assured knowing that the integrity of their building envelope is fully intact and is in no way a liability to public safety. Furthermore, they can be proud to know that their building’s original, historic design intent is preserved and will elongate the lifespan of that original system.
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