Evaluation of Comparative Repair Methods for Stone

Stone masonry, once popular in 19th and early 20th century America, was gradually replaced by concrete and other modern building materials. Many Pennsylvania quarries produced prized local stone such as Pennsylvania Blue Marble, Hummelstown Brownstone, and Chester County Serpentine, all no longer quarried. These materials were used to construct numerous historically significant architecture in the Mid-Atlantic Region. While material authenticity is one of the guiding philosophies for conservation design, oftentimes compromises must be made for many reasons—cost, availability, compatibility with other materials or structure, schedule, skilled labor, aesthetics and an important one which will be the focus of this thesis—durability. Using serpentine as a model, this paper explores alternative methods of non-in-kind repair for buildings constructed with stones no longer quarried in the United States. Two methods are evaluated in detail: Creating a new face or patching using Lithomex, a composite repair material applied directly onto a substrate such as stone or brick. Creating a new face or unit replacement with an available stone such as sandstone, colored with Colorwash Stain, a potassium silicate mineral stain for masonry. An evaluation of repair durability is assessed by comparing surface erosion and color change before and after accelerated weathering. Profile change (profilometry) is assessed through digital models of the samples created with a structural light 3D scanner and color change is analyzed by comparative spectrophotometry. Three case studies of past serpentine repair act as additional discussion of repair methods not evaluated through testing.