San Xavier Mission’s East Tower to Undergo More Exterior Work

The Patronato San Xavier has begun the second phase of work on the East Tower of Mission San Xavier. Scaffolding is going up to facilitate this phase, which will take approximately a year to complete. This is the first major exterior project since the Patronato completed the Conservation Management Plan in 2020.

What does the work on the East Tower entail?

The mission’s walls are built of low-fired brick surrounding a stone rubble masonry core and, historically, were finished with a lime-based plaster. During the first half of the 20th century, the exterior was re-coated with cement-based plaster, a common fix at the time.

It was believed that the less-permeable cement would better repel water and protect the structure. However, these attempts to protect the building by applying cement plaster actually led to damage, including the erosion of parts of the brick substrate, the presence of salt deposits at the interior surfaces, and the detachment of interior plaster.

Encased in a cement-based coating, when water inevitably enters, either through surface cracks or being wicked up into the base of the walls through capillary action, it is unable to escape through the exterior coating. Instead, it exits via the interior surfaces, where the softer lime-based plaster remains. When water vapor exits through a surface, it often leaves behind salt deposits and as those salts solidify and crystalize, creating small areas of physical damage and loss to the surface material.

The Patronato understands that having a compatible and “breathable” lime-based coating is essential in order to allow water vapor to move through the walls without harming the soft brick substrate or interior artwork.

Since the late 1980s, the Patronato has coordinated and funded the removal of nearly all of the cement-based plaster on the exterior. The East Tower is the only portion of the building where it remains. During the work on the East Tower this year, existing exterior plaster that is loose and delaminating from the brick substrate will be removed. Any well-adhered lime-based plaster that remains beneath will be left in place, and the adobe brick substrate will be repaired as necessary. 

Then, the East Tower will receive coats of a more traditional and compatible lime-sand plaster that includes the juice of cactus mucilage, a regional technique that improves the plaster’s workability and its ability to shed water. These traditional plasters let moisture vapor move through the building less destructively, allowing moisture to evaporate from the walls and roof at a similar rate to the underlying substrate.

During the first phase of the $2 million East Tower project (2014 though 2018), important infrastructure work to the foundations and the lower walls was completed.

What about the “missing” dome on the East Tower?

The iconic East Tower was left unfinished in 1797 when construction funds were depleted. Aside from repairs and receiving its new coat of breathable lime-sand plaster, it will be conserved as-is. A true “restoration” might take the upper floors of the tower back to their un-plastered brick appearance. After all, that’s how it would have looked when the structure was “completed” in 1797.

The tower was originally plastered in 1906, during the first major preservation campaign. The goal for the present work is to stabilize the exterior of the building, without seeking to undo what has been done in the past. Similarly, a conservation approach does not justify putting back what was never there, so there are no plans within the project to finish the tower with a dome and lantern.

“Best preservation practice demands protecting what is there, not attempting to interpret what might have been” said Patronato Executive Director Miles Green. “Besides, it’s this asymmetry that in part makes the “White Dove of the Desert so special.”

How is the work funded?

A generous grant to the Patronato from the Fund for Sacred Places provided 15 percent of the East Tower project budget, another 15 percent came from corporations and foundations, and 70 percent is being funded by donations from generous individuals and families. Donations to support this final phase of work on the East Tower can be made to the Conservation and Preservation Fund here:

More about The Patronato San Xavier

The Patronato San Xavier funds and directs ethical conservation, conducts scientific research and interprets the significance of Mission San Xavier del Bac, a National Historic Landmark in the community of Wa:k, part of the Tohono O’odham Nation. Patronato is a non-sectarian non-denominational 501(c)3 and does not receive sustaining support from any government or religious organization. All donations are tax deductible to the fullest extent allowed by law.

In 1978, with destruction of the historic Mission imminent, a group of community leaders formed The Patronato San Xavier, a nonsectarian, nonprofit organization charged with the conservation and preservation of the Mission. Recently that charge was expanded to include conservation research and education. To date, the Patronato has raised and spent over $14 million conserving sections of the Mission.

In 2020, the Patronato funded a new Conservation Management Plan, the first to address needs across the whole Mission footprint and prioritize projects over the next decade.

The next priority is an in-depth study of the iconic façade of the Church in preparation for its conservation.  Other projects include the: mortuary chapel, east convento wing, adobe walls, early-20th century administrative wing, and wooden elements including doors, beams and windows.

National and international recognition of Mission San Xavier and The Patronato San Xavier

1963: Mission San Xavier is designated a National Historic Landmark.

1998: The Patronato receives a National Preservation Award from the National Trust for Historic Preservation citing “painstaking preservation of the interior and exterior of historic Mission San Xavier.”

2012: The Patronato received a Governor’s Centennial Award that acknowledged outstanding  achievements in the preservation or Arizona historic and prehistoric cultural resources during the State’s first 100 years.

2015: The World Monuments Fund adds Mission San Xavier to its “Watch List” of most culturally significant, endangered buildings from around the world.

2019: The Patronato is awarded a grant from The National Fund for Sacred Places, a program of Partners for Sacred Places and the National Trust for Historic Preservation. Preservation of the East Tower is their first project to be funded in Arizona.

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