Soft Capping of Archaeological Masonry Walls: Far View House, Mesa Verde National Park

The control of moisture and temperature fluctuations within masonry walls is critical for conservation of architectural heritage and especially for fragmentary walls within archaeological sites. Exposed compound walls traditionally have been protected by hard cappings of lime, cement, and modified soil mortars. However, hard capping has been found to be inadequate in addressing the long-term management of moisture ingress and thermal movement that will continue to stress and damage the wall. Instead of protecting the wall as initially designed, hard capping can actually accelerate deterioration over time. In order to counter such problems posed by hard capping, a procedure called 'soft capping' has been introduced in recent years at several archaeological sites in England, Turkey and elsewhere. Soft capping replaces hard caps with vegetation planted on top of layers of soil, gravel, and geosynthetics. The idea is to prevent water penetration and to reduce thermal fluctuations by taking advantage of plants' abilities to utilize the water and provide a protective barrier on the wall top. The concept is very similar to green roof technology that has gained increased popularity in recent years. This paper will present laboratory and field-based research conducted on the performance characteristics of soft capping for the exposed masonry walls at Mesa Verde National Park, Colorado. Wall movement, moisture and temperature as well as environmental conditions were monitored to evaluate the effects of hard and soft capping on the test walls.