WYP's Weekly Word
By Bekah Karelis
Glazed Architectural Terra-Cotta
There are many buildings located in downtown Wheeling that have glazed architectural terra-cotta – either large solid blocks, or smaller, more intricately detailed decorative units adorn many of our city’s buildings. The word terra-cotta is derived from the Latin word terra-cotta—literally, "cooked earth." The material was developed during the “Chicago School” of style, as well as part of the High Rise (like Kloss Tower at the corner of 12th and Main) and Beaux Arts styles (like Capitol Theatre on Main Street).
Used mainly architecturally, it is considered the most prevalent material used in our cities. Its popularity lasted from the late 19th century until the 1930s. If you take a look around Wheeling, you will see there are many examples of terra-cotta buildings that have survived, which attests to Wheeling once being an urban center.
Unfortunately, as many of the buildings that were constructed during the terra-cotta craze are reaching the age of 100+ years, the terra-cotta elements on these buildings are starting to deteriorate without proper maintenance.
Here are some common problems with architectural terra-cotta:
Spalling is caused by water trapped in the terra-cotta – perhaps from lack of maintenance, a flaw in the original design, or rising damp caused from a failing roof. In the case of architectural terra-cotta, where the surface is coated in a hard glaze, water is unable to escape because of the coating. The water will build pressure behind the glaze until it pops the hard surface off the face of the terra-cotta. This is called spalling.
Stress-related deterioration is demonstrated by cracks found in terra-cotta blocks. This often occurs in tall buildings. There were methods developed in the later decades of terra-cotta construction that had stress-relieving details built in. Buildings built before these methods were implemented, in many cases, show stress-related deterioration. These cracks can be caused by thermal expansion and contraction, moisture expansion, or building frame shortening.
Crazing is the development of small cracks in the glaze and are typically caused by water retention. As terra-cotta ages, the body of the unit expands due to moisture absorption. The glaze on its surface is not able to expand with the rest of the unit and causes surface cracking. This is not considered a major failure of terra-cotta, though it does increase the water absorption and might cause further deterioration of the terra-cotta unit.
The deterioration of metal anchoring is the most difficult form of damage to diagnose because it is often unseen to the eye. Water that is allowed to enter into the terra-cotta will be trapped and can rust its anchoring system. Once the anchoring system begins to rust, it is only a matter of time before it deteriorates completely, detaching the unit from the building and running the risk that it will fall to the ground.
Terra-cotta is often considered to be one of the most cost-prohibitive materials when restoring an old building. In truth, the costs are high when compared to other items found on an historic building façade. The terra-cotta element was typically cast – and those molds and the companies that made them – did not survive the test of time. So, in order to replicate a damaged piece of terra-cotta, a new mold needs to be created before the it can be molded and fired. Making it even more difficult, is the high percentage of shrinkage that terra-cotta undergoes while it is being fired that can make estimating the end size quite the challenge for a craftsman who creates it.
Luckily, there are more affordable alternatives to create a terra-cotta replacement like stone, fiberglass, and the most promising: glass fiber reinforced concrete (GFRC). The GFRC can easily be cast to recreate the fine details of decorative terra-cotta units. They can also be cast hollow, which makes them a more lightweight option than the original terra-cotta. It can be tinted to match the original color and is the more cost effective option with a quick and easy production.
Considered the “wonder” material of the late 19th and early 20th century, architectural terra-cotta is an important aspect in the history of our building industry and one that should be preserved. Wheeling should take pride in its remaining examples that demonstrate the builders of our city’s respect for this treasured architectural detail!
Major source for this article is the National Park Services's Preservation Brief on historic glazed architectural terra-cotta: https://www.nps.gov/tps/how-to-preserve/briefs/7-terra-cotta.htm