Performance Assessment and Evaluation of Hydrophobic and Ultraviolet Protective Treatments for Historic Log Structures
Historic Preservation and Conservation
This thesis focuses on the evaluation of the durability of traditional and modern sustainable hydrophobic and ultraviolet (UV) resistant treatments for historic log structures such as those found at the Bar BC Dude Ranch in Grand Teton National Park, WY. These treatments are evaluated on a variety of criteria including performance in accelerated weathering, ecological sustainability, and impact on aesthetic and heritage character. Like many log structures in the American West, Grand Teton National Park’s historic structures are exposed to a large amount of UV radiation. In addition to problems delineated from contact with water, the physical fabric of wood is damaged by UV light through degradation of lignin. Exposed wooden members are often affected by this damage in a matter of days. The small depth of penetration restricts damage to surface area. However, when combined with shrinkage and swelling of water sorption or abrasion from weathering, surface material delaminates, exposing untreated surfaces for further delignification and loss of fabric. Accelerated weathering was conducted using a QUV Weatherometer in the Architectural Conservation Laboratory (ACL) which simulates weathering by subjecting samples to cycles of UV-B light, heat, condensation, and sprayed water. While artificial weathering occurs in more intense, concentrated cycles than those in nature, results can be a good indicator of the longer-term performance of the treatments. Five modern and two historically-used treatments were chosen for testing on samples of lodgepole pine (Pinus contorta latifolia), a common building material in the area, obtained from a supplier in the region. Samples were monitored every 100 hours to observe surface degradation and were then evaluated pre- and post-weathering using microscopic analysis, Fourier Transform Infrared Spectroscopy (FTIR), contact angle measurements, and color measurements with a spectrophotometer. Supplementary natural weathering will be conducted on site this summer in order to verify lab results, and the combined results of the lab and field testing programs will inform the Park’s conservation and maintenance program for the many historic log structures in their care. This testing was performed in cooperation with the National Park Service (NPS) and the Western Center for Historic Preservation (WCHP).