San Francisco, CA
The Cathedral of Saint Mary of the Assumption
Completed is 1971, the cathedral is distinguished by its Expressionist design and ascending roof with its cross-shaped apex. Vertical and horizontal openings are filled with Dalle de Verre stained glass windows, constructed with bulk and platted glass set in an epoxy mortar. SGH investigated the cause of mortar deterioration and cracked glass falling from transom and vertical clerestory windows.
SGH led a multidisciplinary team, including a stained glass conservator, to investigate issues with the Dalle de Varre panels. We completed field survey and laboratory analysis, including the following:
- Optical microscopy and scanning electron microscopy (SEM) to observe the condition of the materials
- Chemical analysis using Fourier transform infrared spectroscopy (FTIR) analysis to identify constituents of the mortar matrix and glass adhesive
SGH concluded that the mortar in the transform windows is slowly deteriorating on the outside surface due to ultraviolet (UV) exposure and general weathering. We also determined that the platted glass (multiple glass panes adhered together) is delaminating due to UV degradation of the epoxy-based adhesive and water infiltration could be exacerbating the deterioration.
We recommended the church undertake an immediate protection effort with the assistance of a conservator to remove loose and delaminated glass from the exterior side of the transom panels. We also recommended a topical ultraviolet inhibitor coating to slow the degradation of the mortar matrix.