Consolidation Treatments for the Alveolar Erosion of the Agrillaceous Sandstone at Durham Castle
Historic Preservation and Conservation
The thesis addresses possible consolidation treatments for the sandstone masonry of Durham Castle, a UNESCO World Heritage site located in Durham, England. The historic masonry is made of an argillaceous sandstone that suffers a unique deterioration phenomenon known as alveolar erosion. Alveolar erosion is a problem that relates to the geo-chemical nature of the stone, particularly the presence of swelling clays. Two treatments were considered in this thesis: a plain ethyl silicate (Prosoco OH100), and an elastified ethyl silicate (Remmers KSE 300 E). The performance of each treatment was compared through laboratory testing of the following properties: water absorption and drying, water vapor permeability, color changes, scanning electron microscopy, and drilling resistance measurements. Testing showed that both treatments increased the hardness of the stone, however the stone treated with Conservare OH100 exhibited the greatest increase. Both treatments changed the wetting and drying behavior and the water vapor transmission, with the Remmers KSE 300 E treatment altering the stone slightly more. Through scanning electron microscopy it was shown that both consolidants showed poor adhesion to mineral grains and that Remmers KSE 300 E provided a more uniform coverage than Prosoco OH 100. The application of the latter darkened the surface color of the stone. This thesis shows that there are advantages and disadvantages to each treatment and that additional research is needed to determine if ethyl silicate consolidation will be an effective treatment. Further analysis is needed to determine correlation between binder composition and deterioration. Additionally, it is recommended that pre-treatments, including an anti-swelling agent and adhesive coupling agent be tested in conjunction with the ethyl silicate consolidants.