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 3 of 14

modeling of architectural details as the molds were cast directly from clay prototypes without loss of refinement. Glazed architectural terra-cotta could accommodate subtle nuances of modeling, texture and color. Compared to stone, it was easier to handle, quickly set and more affordable to use. Thought to be fireproof and waterproof, it was readily adaptable to structures of almost any height. The cost of molding the clay, glazing and firing the blocks, when compared to carving stone, represented a considerable savings, especially when casts were used in a modular fashion--that is, repeated over and over again. Maintenance of the fired and glazed surface was easy; it never needed paint and periodic washings restored its original appearance.

With the passage of time, many of the phenomenal claims of the early proponents of glazed architectural terra-cotta have proven true. There are many examples throughout this country that attest to the durability and permanence of this material. Yet present- day deterioration of other significant glazed architectural terra-cotta resources ultimately belie those claims. Why? Historically, the lack of foresight or understanding about the nature and limitations of the material has, in many instances, allowed serious deterioration problems to occur that are only now becoming apparent.

Characteristics of Glazed Architectural Terra-cotta as a Building Material Glazed architectural terra-cotta has many material properties similar to brick or stone. It also has many material properties radically different from those traditional masonry materials. It is those differences which must be considered for a better understanding of some of the material characteristics of glazed architectural terra-cotta when it is used as a building material.

Difficult to identify: Glazed architectural terra-cotta probably comprises one of the largest if not the largest constituent material in some of our urban environments today. However, the infinite varieties of glazing have hidden this fact from the casual observer. One of the attractive features of glazed architectural terra-cotta in its time was that it could be finished (glazed) in exact imitation of stone. In fact, many building owners and architects alike are often surprised to discover that what they presumed to be a granite or limestone building is glazed architectural terra-cotta instead.

-- = Two separate systems: Historically, glazed architectural terra-cotta has been used in %_ - association with two specific and very different types of building systems: as part of a •• ••.~ I traditional load-bearing masonry wall in _~. " buildings of modest height, and as a cladding material in High Rise construction. As cladding, t, ter— i glazed architectural terra-cotta often utilized ti an extensive metal anchoring system to attach it or to "hang it" onto a wall framing system or superstructure. In the first instance the anchoring was limited; in the second, the anchoring was often extensive and complex. Typical construction detail of glazed architectural Likewise, in the first instance, deterioration has terra-cotta ornament. Drawing: Detail, Architectural generally been limited. However, where glazed Terra Cotta, Charles E. White, Jr., 1920. architectural terra-cotta was used as cladding, particularly in high rise construction, present-day deterioration and failure are often severe.

Complexity of deterioration: Deterioration is, by nature of the design, infinitely complex--particularly when glazed architectural terra-cotta has been used as a cladding

http://www2.cr.nps.gov/tps/briefs/briefD7.htm 10/3/2001

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