Mechanisms of Wood Deterioration Several mechanisms of wood deterioration can affect wooden artifacts in cemeteries. These mechanisms, described below, include weathering; moisture; mold and mildew; lichens and moss; decay fungi; insects; and mechanical damage. Weathering Weathering is the result of cyclic wetting and drying and associated distortion of the wood, coupled with exposure to ultraviolet light and erosion by wind-blown debris. Weathering is an extremely slow process but a significant factor in the loss of inscription legibility. The weathering process also changes the appearance of wood and gradually erodes the wood fibers. The erosion of wood fibers due to wind-blown debris (e.g., sand and grit) will vary with height above ground, particle size, and wind velocity, with maximum physical erosion typically occurring less than a foot above the ground. On average, due to the effects of weathering, wooden artifacts can lose up to a quarter-inch of thickness per century of exposure, depending on the wood species. The rate of weathering is greatly influenced by environmental exposure, wood density, climate, and soil condition. We typically think of weathered wood as aesthetically pleasing because it adds an air of authenticity to historic sites, and, unlike decay or insect attack, it seldom damages the wood enough to require replacement (Fig. 3).
Fig. 3. A grave marker with the gray wood typical from UV exposure and weather-caused cracks and checks that allow moisture penetration.
Annual Journal of the Association for Gravestone Studies