Testing terracotta in the United States: early testing practices and modern conservation.

Cracks, spalls and efflorescence are unsightly, but what do they say about the service life of a terracotta unit? And what analytical tests can we perform to help us define its life span? Unfortunately, in the case of architectural terracotta, determining if a deteriorated unit has nearly reached the end of its useful life is not entirely straightforward. Simply looking at the surface of a terracotta unit does not provide sufficient information to characterize its durability, nor does repairing the surface guarantee its survival. The large-scale manufacturing of architectural terracotta in the US began in the 1870s. By 1876, magazines such asAmerican Architect and Building Newsmarketed terracotta as a good, ‘durable’ material for use on cornices. Within two decades, however, concerns about the performance of the building material were raised with respect to glaze adhesion, spalling, and physical strength. Extensive research was undertaken by the author on architectural terracotta testing practices and manufacturing methods used historically throughout the US. With literally hundreds of tests carried out and published between 1899 and 1961, it seemed that no one test was able to fully address the complex question of durability. In an effort to understand the relationship between physical characteristics and durability, several historic glazed terracotta units, all taken from buildings constructed before 1938, were subjected to microscopic examination, water vapor transmission (WVT) measurement, freeze thaw testing and glaze adhesion. The article examines the results, the limits of the individual tests, and how a variety of evaluation techniques are required – in combination – to understand the structure and condition of the material. There is also a brief discussion of modern repair techniques and whether these repairs are appropriate or even worthwhile. [ABSTRACT FROM PUBLISHER]