Preserving Spanish Colonial Mission's Masonry at San Antonio Missions National Historical Park

Two craftsmen with the Historic Preservation Training Center work on the Espada Aqueduct.

NPS Photo/Andrew Shirey

In January 2026, skilled craftspeople from the National Park Service’s Historic Preservation Training Center were hard at work performing important maintenance and preservation on several Spanish colonial structures within San Antonio Missions National Historical Park. These locations and work included:

• Espada Aqueduct
• Mission San Juan
• Mission Espada

This project is funded through the Legacy Restoration Fund (LRF), as authorized by the Great American Outdoors Act (GAOA), via the Historic Preservation Training Center.

At the Espada Aqueduct, using traditional techniques and materials, the preservation team carefully filled and repaired small cracks and fractures in the historic plaster to help reduce water leakage and protect the structure for future generations. Built in the 1740s, the Espada Aqueduct is the oldest Spanish colonial aqueduct still in operation in the United States. It once carried water from the San Antonio River to Mission San Francisco de la Espada to power farming, ranching, and community life. Today, it continues to tell the story of engineering ingenuity, indigenous labor, and mission-era agriculture all while still carrying water!

Crew of masons working on the Mission San Juan wall.

NPS Photo/Andrew Shirey

A peek into project details:

Following the pre-construction meetings upon arrival at San Antonio Missions, the masonry crew began masonry repairs at the San Juan Mission boundary wall. In preparation for the other site at the Espada Aqueduct, the crew conducted inspections, vegetation removal, installation of sluice gates and sandbag dams, and substantial drainage and cleaning of the aqueduct channel for their work to begin there soon.

Interior aqueduct surfaces were cleaned, inspected, and repaired, including sectional patching and crack stabilization, while exterior joint inspections and initial repointing at Mission San Juan Mission progressed. Continued aqueduct waterproofing preparation and masonry repairs continued throughout their weeks in the park.

In their final site of work, the preservation crew moved to Mission Espada to install new cedar log lintels at the circa 1700's Indian Quarters. New cedar lintels were installed in the historic masonry and the wood was treated with a water resistant wood sealant. The lintels were installed with the bedding/pointing mortar recipe used for wall repairs at Mission San Juan.

The current work and phase of repointing work is a continuation of preservation work that was started by San Antonio Missions mason employees between 2021 - 2024.

Two important parts of this work include repointing and capping. Both of these are essential to keeping historic masonry strong and protected.

What is repointing?

Repointing involves carefully removing deteriorated mortar form construction joints (brick, stone, block...etc) and replacing it with a compatible lime-based mortar. This helps keep water out of the walls while allowing the stone to breathe and is an important feature of historic masonry that modern materials can't replicate.

What is capping?

Capping protects the tops of walls by adding a protective layer that sheds water away from the stone. Without proper capping, rain can seep into the masonry walls from above, mortar erosion, structural fractures and longterm damage. Using historically appropriate materials and methods helps ensure that Mission San Juan's walls remain stable while honoring the craftsmanship and knowledge of the original builders. Many of whom were Indigenous artisans whose skills shaped these structures.

From the Espada Aqueduct to the mission compounds themselves, the skilled masonry craftspeople of the National Park Service’s Historic Preservation Training Center are safeguarding San Antonio’s Spanish colonial heritage. By using time‑tested techniques and compatible materials to address hairline cracks, plaster losses, and other age‑related vulnerabilities, their meticulous work reduces water intrusion, stabilizes historic finishes, and prevents small issues from becoming costly structural problems—helping ensure that the nation’s oldest still‑operating Spanish colonial aqueduct and its surrounding mission landscapes remain stable, safe, and living history for generations to come.

In a park recognized for preserving one of the most complete, geographically concentrated ensembles of Spanish colonial mission complexes in the world, this hands‑on preservation is more than maintenance; it protects the integrity of places where engineering ingenuity, indigenous labor, and mission‑era agriculture continue to tell a layered story of community and resilience.

Winter Freeze Brought Unusual Ice Challenges

Left image
Sheet Ice on the Espada Aqueduct.
Credit: NPS Image

Right image
Water fully restored a couple days later in the repaired Espada Aqueduct.
Credit: NPS Image

On January 26, 2026 the Historical Preservation Training Center crew reported to the Espada Aqueduct on a below-freezing morning to pump out standing water and sheet ice from the irrigation channel that had accumulated within the aqueduct basin from the Saturday/Sunday freezing rain.