[De]constructing Guastavino Vaulting

This thesis analyzes the mortars used in the construction of Guastavino tile vault assemblies through an in-depth study of St. Paul’s Chapel and observations at five other Guastavino projects. Limited research has been published that addresses the mortars used in Guastavino vaults, but the available literature indicates that only gypsum mortar and Portland cement mortar were used in their construction. Furthermore, literature establishes that vaults were assembled by installing the first layer of tiles with gypsum mortar, while the above tile layers were set in Portland cement mortar. Preservation professionals often encounter discrepancies between this assembly described in literature and the assemblies and mortars observed during restoration projects. To address these discrepancies, this thesis performed a material study at St. Paul’s Chapel, identifying the mortars and their assembly through archival review, physical observation, and cursory petrographic analysis of select samples. It was determined that at least four different types of mortars, including gypsum mortar, gypsum-lime mortar, natural cement mortar, and portland cement mortar were used in the construction of St. Pau