A Performance Evaluation of Amended Stabilization Mortars at Wupatki National Monument, Arizona

Earthen mortars are commonly amended to display ‘improved’ performance and weathering properties than unamended soil mortars. In an effort to make more lasting repairs, the National Park Service (NPS) has used amended earthen mortars on their historic structures since the 19th century. These interventions have displayed various levels of compatibility with original masonry material. One such amendment, the acrylic emulsion Rhoplex™ E-330, has been used in setting and pointing mortars for the conservation of ruin sites at multiple National Parks since the 1970s. This paper focus on conservation repair mortars, specifically the durability and performance of amended earthen mortars at the Wupatki Pueblo. Located in north-central Arizona, near Flagstaff, Wupatki National Monument consist of multiple sites with the Wupatki Pueblo dating to ca. 1100 AD. Built upon a natural outcropping, the pueblo is constructed of coursed rubble stone, predominately of the local Moenkopi sandstone, all laid in an earthen mortar. Since 1924, the monument has been administered by the National Park Service with restoration and stabilization work continuing to today. This research examines conservation soil-based mortars at archaeological sites with Wupatki Pueblo serving as the case study. Research includes analyzing and characterizing the composition of past and current stabilization mortars used on site, assessing their overall compatibility with the masonry, and creating test formulations to provide recommendations for future use. Test formulations evaluate the effects of acrylic polymers on Wupatki’s current soil supply with only the ratio of Rhoplex™ E-330 to water altered in each formulation. Physical and mechanical tests performed on these mortar formulations provide insight into how these mortars perform in the field. Ultimately, these efforts provide the NPS with an optimal amended stabilization mortar formulation that is compatible with the Wupatki Pueblo’s original masonry system.