Tumacácori National Historical Park

Since 2017, the Center for Architectural Conservation (part of the Preservation Research Collaborative at Penn) has been leading conservation efforts on the original lime plaster and gypsum finishes of Mission San José de Tumacácori, located one hour south of Tucson, Arizona. The Mission Church, part of the Sonoran Mission Chain established by Padre Eusebio Kino in the late 16th/early 17th century, is one of the oldest surviving 18th-century Spanish Mission churches in the American Southwest and also the first Spanish Colonial mission site to receive national recognition (1908) for its remarkable architecture and decorative painting.

The last comprehensive conservation work on the church interior took place in 1984. In the decades since, the plasters have undergone significant deterioration. More than 6,000 square feet of original Franciscan-era plaster remain within the lower sanctuary and nave, and the baptistery and sacristy retain nearly 100% of their historic finishes. However, recent condition assessments revealed widespread failure of past repair campaigns meant to reattach plaster to the adobe substrate, along with new cracking and weakened plaster keys identified through photogrammetry. The earthen mortar and adobe walls continue to disintegrate, risking further loss of adhesion between substrate and surface finishes. In some areas, the adobe at floor level is receding at an alarming rate of approximately ¼ inch per year, resulting in irreversible detachment and loss of plaster. The loss of plaster from higher elevations also presents serious public safety hazards.

Current conservation treatments involve removing incompatible materials, such as cement infills, and stabilizing the historic plasters using gelatin facings, earthen and lime grout injection, and mortar edging. Beyond its preservation goals, the project provides a valuable platform for graduate students to engage in hands-on, “real world” training under the guidance of faculty and professional conservators from the NPS and regional academic and conservation institutions. In addition, the project incorporates public outreach to help visitors understand the science and challenges of preserving Spanish Colonial surface finishes, expanding the impact of the work beyond the professional conservation community.