Terra-cotta maintenance and repair guide, undated

NYC 9/11 Public Portal Document

Preservation Brief 7: The Preservation of Historic Glazed Architectural Terra-Cotta Page 1 of 14

Preservation Briefs 7 Technical Preservation Services National Park Service

The Preservation of Historic Glazed Architectural Terra-Cotta de Teel Patterson Tiller

*What is Terra-Cotta »Types of Terra-Cotta >> Characteristics of Glazed Architectural Terra-Cotta »Common Deterioration Problems *Deterioration Inspection and Analysis *Maintenance, Repair and Replacement *Summary »Further Reading

Glazed architectural terra-cotta was significant in the development of important architectural idioms in this country--specifically, the "Chicago School," the High Rise and the Historic or Beaux Arts styles. In fact, glazed architectural terra-cotta is one of the most prevalent masonry building materials found in the urban environment today. Popular between the late 19th century and the 1930s, glazed architectural terra-cotta offered a modular, varied and relatively inexpensive approach to wall and floor construction. It was particularly adaptable to vigorous and rich ornamental detailing. However, with changing vogues in materials and architectural styles and rising production costs, glazed architectural terra-cotta fell into disfavor and disuse by the mid 20th century.

Today, information on the maintenance, rehabilitation and replacement of glazed architectural terra-cotta is limited, as are sources of new glazed architectural terra-cotta. This report, then, will discuss some of the major deterioration problems that commonly occur in historic glazed architectural terra-cotta, methods of determining the extent of that deterioration and recommendations for the maintenance, repair and replacement of the deteriorated historic material.

What is Terra-Cotta? 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.

http://www2.cr.nps.gov/tps/briefs/brief07.htm 10/3/2001

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