Adobe Bricks

Building Blocks of a Mission

Left image
An artist's rendering of adobe bricks drying in the sun.

Right image
Replacement adobe bricks curing in the sun.

 

• Mud

  
  

  The humble mixture of dirt and water forms the foundation of every built structure at Tumacácori.

  Date created:

  10/14/2020

  Audio Transcript

  mud squishing/splat

 

How It Was

During mission times, people spent countless hours creating adobe bricks to build the church and other buildings. The O'odham also used earthen construction technology to build houses made of soil, water, grass, ocotillo and mesquite. In fact, earthen architecture dates back many thousands of years in the archeological record.

An "adobe" or "adobe brick" is a dried-mud brick made of earth, water and usually some kind of organic binding material like straw or grass. The word "adobe" comes from Egyptian, which was adopted into Arabic, then into Spanish, and now enjoys common usage in English. Adobe is one of the world's oldest and most effective building materials because of its ability to flex under changing temperatures, and to keep interior environments cool in hot climates.

Some of the adobe bricks at Tumacácori contain traces of "caliche," a type of calcium carbonate deposit found in the soil in the hills near the mission. Caliche helped hold the adobe mud together. The mud was mixed to a consistency similar to peanut butter. The prepared mud was placed into forms, tamped, leveled, and placed in the sun to dry before being used. Some of the adobe bricks were fired (cooked in kilns) which made them stronger. These fired adobe bricks were used in places where greater strength was needed for support, such as in the top of the bell tower.

Adobe construction has low tensile strength, so bricks needed for multiple stories were made thick. A typical size of an adobe brick used in the Tumacácori church was 12x3x24 inches, and workers had to make about 90,000 bricks to construct the church.

This long tradition of constructing buildings using natural materials has survived and evolved over the centuries with the influence of many cultures. It continues to be preserved today at Tumacácori.

 

How It Is Now

Since Tumacácori was declared a national monument in 1908, it has undergone many preservation and stabilation efforts in order to maintain the adobe brick structures. Early preservation efforts replaced the church roof, rebuilt a gaping hole in the bell tower, and replaced the curved pediment over the facade. The planhas always been to stabilize the structure, not rebuild it. Approximately seventy percent of the adobe bricks in the church are original.

Some earlier efforts at restoration, such as using cement to repair the structures, were not successful. Modern materials such as cement, vinyl, or acrylic-based materials are incompatible with the mud-based adobe due to differing expansion and shrinking characteristics which can result in cracking and breaking. Historically, most adobe bricks were mortared together with mud. This type of mortar weathers with the same rate of expansion, contraction and deterioration as the bricks, making mud-based mortar the best material for bonding historic adobe bricks.

Research on preservation and stabilization is at the heart of Tumacácori's adobe maintenance efforts today. Ongoing research continues, seeking the best methods of adobe construction and preservation, and the park staff uses this information to maintain the historic buildings in the park and to make replacement adobes for park structures.

 

Learn More

Tumacácori's Preservation Program