The dome of St. Mary's Chapel had multiple sources of decay, beginning with seismic damage, which allowed moisture to seep into the interior and delaminate the dome structurally. Stabilizing the concrete underpinning was required before new solid-body porcelain tile installation, to match the original decorative surface design, but in the new much more durable material.
We recrafted the medallions offsite. Using full scale drawings, we were able to reproduce the design elements in reverse, setting each tessera in a water-soluble adhesive on top of the pattern, and segmented for easier installation. These paper-backed design motifs were then transferred to the job site for final installation on each of six faces on the dome, using thin-set adhesive. The water-based glue keeping the paper pattern in place could then be removed by soaking in water and rinsing with pressurized water. Once all tiles were installed, the medallions were rinsed with water to loosen the water-based glue residue, and the paper and residue removed. Grouting could then take place on the entire dome to complete the restoration.