Repairing Glazed Terra Cotta at Hoyt Sherman Place, Des Moines

First published in 2009 in "Exceptional Places," a newsletter of the National Park Service's Midwest Region Division of Cultural Resources, by Mark Chavez.

What terra cotta is

The National Park Service's Preservation Brief No. 7: The Preservation of Historic Glazed Architectural Terra Cotta, by de Teel Patterson Tiller, describes the material this way:

• The clay. Terra cotta, from the Latin for "cooked earth," is high-grade weathered or aged clay mixed with sand or ground fired clay, then molded and fired at high temperatures to a hardness and density brick cannot reach. Put simply, it is an enriched molded clay brick or block. Its color, from red and brown to white, depends on where the clay comes from and its type.
• The block. It was usually cast hollow, in blocks open at the back like boxes, with internal stiffeners called webbing that made them much stronger without adding much weight.
• The glaze. Before firing, the air-dried block was often brushed or sprayed with a slip glaze (a clay wash) or a solution of metal salts. The glaze changed the color, imitated other finishes, and made the weather face nearly impervious. Well maintained, it weathered very well, resisted chipping and fading, and gave designers an unlimited range of colors; few building materials still match its range and durability.

Hoyt Sherman Place

Hoyt Sherman Place in Des Moines, Iowa, built in 1877, is an entertainment and education center listed as nationally significant in the National Register of Historic Places.

Hoyt Sherman was born in 1827 in Lancaster, Ohio, into a prominent political family. His father, Charles R. Sherman, sat on the Ohio Supreme Court. His older brothers included Charles Taylor Sherman, a federal judge; U.S. Senator John Sherman, of the Sherman Anti-Trust Act; and Major General William T. Sherman of the Civil War. Hoyt Sherman arrived at the frontier post of Fort Des Moines in 1848 and was soon appointed its postmaster.

According to Hoyt Sherman Place, he built the town's first post office and bank, served on the town council and was deeply involved in local and state politics. At the start of the Civil War, President Lincoln made him an Army paymaster with the rank of major. Afterward he helped found the Equitable of Iowa Insurance Company, and gave counsel, time and money so that Des Moines would have schools, a college, a waterworks and more.

In 1877 he built a grand house on what was then the western edge of Des Moines, and lived there until his death in 1904. It stood empty until 1907, when the Des Moines Women's Club took it over as a clubhouse. The club promoted the city's cultural life, sponsoring events and speakers including Amelia Earhart, Helen Keller and Grant Wood. It added a gallery, the first public art museum in Des Moines, and a 1,400-seat theater completed in 1923.

The house is still an art museum, showing 19th- and 20th-century paintings and preserved interiors and artifacts from Sherman's time, and the restored theater is still a performance hall. The Sherman Hill historic neighborhood takes its name from the place.

The repairs

In 2005 Hoyt Sherman Place received a Save America's Treasures grant for a long list of work: masonry repair and tuckpointing, roofing over the stage, new gutters and downspouts, restoration of wood windows and trim, the leaded glass windows of the theater mezzanine and the main entry canopy, dormer siding, brick paving, the clay tile parapet cap, landscape features such as the sidewalk, steps, a wall and brick piers, and the terra cotta.

The terra cotta patching went step by step:

1. Find the damage. Deteriorated material was located by tapping gently with a small hammer, and removed.
2. Prepare. Surfaces to be patched were rinsed and left damp, then brush-coated with a slurry of patching compound.
3. Build up. Patching compound went on in layers, each roughened to give the next one a key.
4. Shape. At the surface, the patch was troweled, scraped or carved to match the texture, details and contours of the surrounding terra cotta.
5. Cure. The patch was kept damp for 72 hours or until the compound set.
6. Glaze. A special glaze was applied to the manufacturer's instructions. It took two coats to match the neighboring units, with architectural stippling done with an artist's brush between coats.

Sources

• National Park Service, "Terra Cotta Repair": https://www.nps.gov/articles/terra-cotta-repair.htm
• National Park Service, Save America's Treasures grants: https://www.nps.gov/subjects/historicpreservationfund/save-americas-treasures-grants.htm
• The NPS article spells the author of Preservation Brief No. 7 "Tille"; this page uses "Tiller."
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.