Terra Cotta Repair

White terra cotta piece with chunks missing.
Spalling is a common condition caused by water infiltration and freezing temperatures.

Photo courtesy of Preservation Brief No. 7.

Preservation Brief No. 7: The Preservation of Historic Glazed Architectural Terra Cotta, by de Teel Patterson Tille, provides the following definition of the material:
“Generically, the broadest definition of terra cotta refers to a high grade of weathered or aged clay, which when mixed with sand or with pulverized fired clay, can be molded and fired at high temperatures to a hardness and compactness not obtainable with brick. Simply put, terra cotta is an enriched molded clay brick or block. The word terra cotta is derived from the Latin word terra cotta — literally, “cooked earth.” Terra cotta clays vary widely in color according to geography and types, ranging from red and brown to white.

Terra cotta was usually hollow cast in blocks which were open to the back, like boxes, with internal compartment-like stiffeners called webbing. Webbing substantially strengthened the load-bearing capacity of the hollow terra cotta block without greatly increasing its weight.

Terra cotta blocks were often finished with a glaze; that is, a slip glaze (clay wash) or an aqueous solution of metal salts was brushed or sprayed on the air-dried block before firing. Glazing changed the color, imitated different finishes, and produced a relatively impervious surface on the weather face of the final product. The glaze on the terra cotta unit possessed excellent weathering properties when properly maintained. It had rich color and provided a hard surface that was not easily chipped off. Glazing offered unlimited and fade-resistant colors to the designer. Even today, few building materials can match the glazes on terra cotta for the range and, most importantly, the durability of colors.”

Hoyt Sherman Place

Hoyt Sherman Place, a grand entertainment and education facility in Des Moines, Iowa, was originally built in 1877, and is a nationally significant National Register of Historic Places property. Its name sake was integral in the development of Iowa’s political system in the mid-19th century. Hoyt Sherman was born in 1827 in Lancaster, Ohio, to a prominent family within the state’s political forum. His father was Charles R. Sherman, Judge of the Ohio Supreme Court. Sherman’s older brothers also achieved great political recognition—Charles Taylor Sherman, a US Federal Judge, US Senator John Sherman of the Sherman Anti-Trust Act, and Major General William T. Sherman of Civil War fame. Hoyt Sherman attained his own political recognition —he was appointed postmaster of Fort Des Moines shortly after his arrival to the frontier post in 1848.

According to the Hoyt Sherman Place website, Sherman built the first post office and bank, served on the town council and was very involved in local and state politics. President Lincoln appointed him Army paymaster at the start of the Civil War with the rank of Major. Upon his return, Sherman teamed up with others and created Equitable of Iowa Insurance Company. During this time he also gave his counsel, time, and money to ensure that Des Moines had schools, a college, a waterworks system and many more facilities.

Sherman built a grand manor in 1877 on the then-western boundary of Des Moines, where he lived until his death in 1904. The mansion remained vacant until 1907, when the Des Moines Women’s Club took charge of the facility, using it as their clubhouse. The women of the club were leading stewards in promoting cultural heritage throughout the city, sponsoring cultural events and speakers, including Amelia Earhart, Helen Keller, and Grant Wood. They subsequently added a gallery to the building, which became the first public art museum in Des Moines, as well as a beautiful 1,400-seat theater that was completed in 1923. The mansion still functions as an art museum, displaying collections of 19th- and 20th-century paintings and beautifully preserved interiors and artifacts from Sherman’s era.

The theater was recently restored and continues to be used as a performance hall. Hoyt Sherman Place is the namesake for one of Des Moines’ historic neighborhoods—Sherman Hill.
One image of a damaged stone column and the other of the same repaired.
Left: column capital before restoration. Right: column capital after restoration.

Photo courtesy of GE Wattier Architects, Inc.

Repair Work at Hoyt Sherman Place

In 2005, Hoyt Sherman Place received a Save America's Treasures grant for a number of repairs. These included masonry repair and tuck pointing; roofing repair over the stage; replacement of gutters and downspouts; restoration of wood windows and wood trim; restoration of leaded glass windows at the theatre mezzanine; restoration of the main entry canopy; repair of dormer siding; base brick paving repairs; repair/replacement of clay tile parapet cap; repair/replacement of landscape features including the sidewalk, steps, wall south of the theater, and brick piers at southeast entrance; and repair/replacement of terra cotta features.

Included in this article are some photos of terra cotta repairs done at Hoyt Sherman Place. The process entailed removal of deteriorated material as determined by sounding gently with a small hammer; rinsing of surfaces to be patched and leaving damp; brush-coating surfaces with slurry coat of patching compound; and placement of patching compound in layers which had been roughened to provide a key for the next layer. Once the patching compound reached the surface or finished edge, it was troweled, scraped, or carved to match the texture, details, and surrounding surface plane or contour of the existing terra cotta.
One image of damaged stone. The other of repaired stone.
Left: door jamb before restoration. Right: door jamb after restoration.

Photo courtesy of GE Wattier Architects, Inc.

The patch had to be kept damp for 72 hours or until the patching compound had set. After the final layer of patching compound had cured and was shaped, a special glaze was installed according to the manufacturer's written instructions. Two coats were needed to match the glaze of adjacent terra cotta units, and architectural stippling was performed using an artist’s brush between glazing sequences.
Originally published in "Exceptional Places" Vol. 4, 2009, a newsletter of the Division of Cultural Resources, Midwest Region. Written by Mark Chavez.