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Conservation And Preservation Of Stained Glass Nationwide
The east and south elevations of St. Dominic’s Church. A typical Gothic pointed arch window. A vertical crack in a terra cotta mullion.

Integrating Terra Cotta Window Mullion Repair
With Leaded Stained Glass Window Restoration - Part 1

St. Dominic’s Church, San Francisco

The Stained Glass Quarterly
by Lex F. Campbell; Simpson, Gumpertz, and Heger

Introduction

St. Dominic’s Church in San Francisco, CA, is in the process of completing a multi-phased terra cotta and leaded stained glass window restoration project. With the ambitious objective of restoring more than 90% of the window openings and leaded glass window panels in the Church, the project encompasses more than 70 openings, including windows as large as the 21 x 31 ft. Christ in Glory tracery window to smaller 3 x 5 ft. arched amber glass windows. Nearly all of the windows were experiencing deterioration of terra cotta mullions that frame the lancet openings and support the Gothic tracery. Concurrently, much of the leaded glass was experiencing significant problems with lead and glazing deterioration.

Remarkable in scale for a parish of its size, the restoration project provides valuable lessons in some of the complex issues encountered in integrated terra cotta cladding and leaded glass window restoration. This paper will identify typi-cal problems of deterioration encountered in terra cotta window tracery systems. Furthermore, it will emphasize the importance of integrating the terra cotta and stained glass setting in order to provide a watertight system. Understanding the nature of terra cotta construction; identifying underlying causes of deterioration; designing effective repairs; and planning and close coordination between trades have all contributed to a successful restoration that is now nearly complete.

Terra Cotta and Gothic Revival Architecture

Architectural terra cotta was a common construction material in the United States during the first half of the twentieth century. Made from fired clay typically with a ceramic finish, terra cotta formed a durable facing material with unique functional and ornamental potential. At the functional level, terra cotta blocks were commonly used as wall facing and on cornices to provide durable weather protection. Aesthetically, buildings were visually enhanced by the unique colors formed by glazes. Terra cotta offered countless numbers of shapes and was able to articulate any number of architectural styles.

Perhaps best known for its utilization as ornamentation and facing on commercial buildings, terra cotta was also especially applicable to church construction. The highly sculptural clay material, which was formed from sculpted molds, made it ideal for the intricate ornamentation and sculpture of Gothic Revival churches in particular. Tracery windows were no exception, with terra cotta used to form jambs, mullions, and elaborate tracery work.

In some ways, the simple configuration of terra cotta block window construction is similar to traditional masonry coursing. The sill supports stacked mullion or jamb blocks, which, in turn, sup-port a spring stone and tracery blocks within an arch. However, the nature of terra cotta is different from stone in sever-al important ways. Primarily, terra cotta blocks are hollow and require structural reinforcing most often comprised of steel and grout fill. Terra cotta, which is not load bearing, generally is anchored to the structural frame. The exterior and interior wall facings, often of different materials leave a groove (or rebate) in between for the window placement. Grout fill is often installed in the terra cotta cavities to form solid blocks as well as to provide additional structural stability.

As opposed to monolithic stone block coursing, terra cotta construction is instead an assembly of components each with specific function and potential problems and rehabilitation issues to address. As we will see, these factors may significantly impact restoration approaches to tracery window restoration from restoration sequencing and window removal to the final setting and the configuration of the support matrix.

The Stained Glass Quarterly

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