This paper focuses on the evaluation of the durability of traditional and modern 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 being evaluated on a variety of criteria including performance in accelerated and natural weathering testing, ecological sustainability, and impact on aesthetic and heritage character. The testing was performed at The Architectural Conservation Laboratory (ACL) at the University of Pennsylvania in cooperation with the National Park Service and the Western Center for Historic Preservation (WCHP), and the University of Wyoming. Natural weathering is currently being conducted on site in Grand Teton National Park, having been set up in early August for an initial year-long testing period, in order to verify lab results and develop a treatment protocol for local log structures that will preserve original fabric while maintaining intended aesthetics of the buildings.
Like many log structures in the American West, the Northwestern National Park Region’s historic structures are exposed to a large amount of UV radiation due to high elevation. In addition to degradation mechanisms delineated from contact with water, the physical fabric of wood is damaged by UV light through degradation of lignin, essentially the glue that holds the cellulose fibers together. 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. This process is very slow but causes a steady loss of original fabric on historic log structures. Accelerated weathering was conducted in Spring of 2015 using a QUV Weatherometer at the ACL which simulates weathering by subjecting samples to cycles of UVB ultraviolet light, heat, condensation, and water spray. While artificial weathering occurs in more intense, concentrated cycles than those in nature, results can be an indicator of longer-term performance of the treatments and the substrate. Five modern and two historically-used treatments were tested on new samples of lodgepole pine (Pinus contorta latifola), a common building material in the area. Samples were evaluated using a range of methods including weight change, surface degradation, color changes, changes in water repellency, and FTIR in an effort to determine performance during testing. A natural weathering rack was designed and constructed on site in the summer of 2015 in order to verify or deny results found in lab testing. Both weathered and new samples of lodgepole pine logs were treated with those treatments that performed well in accelerated weathering and were fixed in place on the bracket after being evaluated for starting weight, color, surface appearance, and water repellency. The weathering period will continue for a year, a full cycle of seasons, before extensive evaluation, but color measurements and photographs are being taken at intervals during the process.The combined results of the lab and field testing programs can inform the Park’s conservation and maintenance program for the many historic log structures in their care.