Assessment and Evaluation of Consolidation Methods on Serpentine Stone at the 19th Street Baptist Church, Philadelphia, PA
water vapor transmission
scanning electron microscopy
Historic Preservation and Conservation
Serpentine (serpentinite) is a notably unique building stone from Chester County, Pennsylvania that enjoyed regional building popularity in and around Philadelphia, New York, Washington, and Baltimore. A hydrous magnesium silicate metamorphic rock, its unusual green color and luster expanded the Victorian palette and love of polychromatic masonry popular during the last quarter of the nineteenth century. However, its generally poor weatherability in the city environment and discontinued availability now argue for greater study of its conservation possibilities. This research examines the composition and performance of weathered serpentine at the 19th Street Baptist Church in Philadelphia, Pennsylvania to determine the possible efficacy of ethyl silicate consolidation treatments in improving stone performance and resistance to weathering. The 19th Street Baptist Church is an early and important ecclesiastical design by the famous Philadelphia architecture firm of Frank Furness and George Hewitt and one of only a few serpentine buildings that survives in and around Philadelphia due to the deteriorative nature of the stone. The serpentine poses a challenge due to its complex mineralogical and textural composition, narrow range of use, and lack of previous scientific research conducted on the material. Considering the nature of the serpentine stone, consolidation was tested to restore material integrity by recreating the inter-granular cohesion the stone lost through weathering without aesthetic alterations. Research and testing was informed by a detailed conditions survey of the exterior stone of the church as well as characterization of the stone through petrographic thin section analysis, SEM analysis, and wet chemical methods (acid solubility and salt tests). Physical testing of the stone properties (durability, absorption rates, porosity, etc.) were measured before and after consolidation through water absorption, water vapor transmission, freeze/thaw resistance, and strength by resistance drilling. The results of this test program provide recommendations for future conservation options for the 19th Street Baptist Church and other serpentine buildings throughout metropolitan areas in the Mid-Atlantic and South Atlantic regions.