20907 Acorn Ave. Milton, Iowa • 641-675-3740
Conservation And Preservation Of Stained Glass Nationwide
A lancet window with new brass tee bars. Interior of lancer panel showing brass round bars. Detail of tee bar connection.

Integrating Terra Cotta Window Mullion Repair
With Leaded Stained Glass Window Restoration - Part 5

St. Dominic’s Church, San Francisco

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

Supporting tee and round bars also were originally set in the mortar-filled reglet. Because of water penetration, the mortar was often cracked and loose, decreasing the stability of the support bars and thus the windows. Due to the moisture infiltration of the reglet joint and subsequent damage to the mullions and windows, it was concluded that the existing mortar window setting was inadequate for a window set in a terra cotta assembly. A more watertight joint would be necessary.

To achieve a watertight and flexible joint, the mortar-filled reglet was replaced with a sealant joint. From the outside, the leaded glass panels were secured against the back of the reglet against the interior cast stone with a strip of glazing tape in between. A silicone sealant joint with backer rod was installed in the remaining gap, which averaged ¾” wide. Standard pull tests of the sealant were used to verify adequate adhesion to the terra cotta and glass.

The restored window lancet panels were secured with new bronze tee and round bars. The tee bars were mechanically attached to the interior stone with flanges and sockets bolted to the stone. The setting configuration allows for the removal of individual lancets panels if required, as well as the replacement of individual bars.

Overall, the new window setting provides waterproofing and structural advantages over the original mortar setting. The properly designed sealant joint (with two-sided adhesion) will provide an adequate barrier to water penetration. The joints also proved some flexibility in the event of movement between different materials. The sealant joint and windows are serviceable with less effort and cost than the tradition mortar setting. With proper maintenance of the joint, the terra cotta and windows will remain in good condition for the foreseeable future..


In conclusion, detailed survey information, careful planning and sequencing, and repair designs responsive to the existing conditions have helped ensure a successful project. Specifically, this project addressed the conditions and special need defined by a terra cotta clad window opening and leaded glass assembly. Loose and cracked terra cotta mullion blocks were replaced. Structural steel was replaced with a more durable stainless steel material. A properly designed sealant joint will remedy waterproofing concerns, a root cause of both window and mullion problems. All the repairs remained sensitive to the historic character of the building and leaded glass panels. Finally, through priority sequencing, the work has occurred at a pace compatible with annual Church fundraising and budges. Through the exceptional efforts of the Church and project team, this important landmark has been preserved for future generations. St. Dominic’s is scheduled to complete the window restoration in 2010, with more than 70 windows completed.

1. Window Survey. Femenella & Associates, Inc.,
Branchburg, New Jersey. Submitted to Simpson, Gumpertz and Heger, San Francisco, California.

The Stained Glass Quarterly

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