The Adobe--Part 1 Gordon Rottman

The Adobe—Part 1

The adobe building was the most common shelter in the old southwest. They were a great deal more common that the wood-frame and plank ranch houses with wooden shingle roofs depicted in Western movies sitting in the middle of desert. was too far from sources of scare trees and sawmills. Besides the excessive raw materials costs, freight transport was high.

Adobes were common in south and west Texas, northern Mexico, and the southern portions of New Mexico, Arizona, California, and elsewhere. These places are characterized by hot dry climates and so happened to possess an abundance of the raw materials necessary to make adobe mud—dirt.

The word goes back to at least 2000 BC, the ancient Egyptian dbt for mud brick with the modern spelling coming from Old Spanish.

Part 2, Raising an Adobe House, will appear here on July 21, Monday.

Simple adobes under construction. Note the modern tile roofs.

Morelos, Coahuila

I took an interest in adobe construction after examining buildings and compound walls in Morelos, Coahuila in northern Mexico, my wife’s hometown. The town and the other four towns of Los Cinco Manantiales—the Five Springs—are about 30 miles across the border from Eagle Pass, Texas. The communities were established some 170 years ago and some original adobes still in use. We have relatives living in adobe homes build around or even before the turn of the century (the one before this last one). They’re structurally sound and built like forts. They’ve been modernized of course with electrical outlets, lighting, water and sewer lines. Many are now air conditioned. Most have the original exterior plaster, although this occasionally requires patching. In most cases the original interior plaster was removed and a more durable concrete-based plaster applied. The floors in most are a layer of adobe bricks overlaid with attractive title. In a few instances the base bricks broke up and were replaced by poured concrete with iron rebar, sometimes after laying water and sewer lines. In the old days a smooth layer of thick plaster was laid on the floor bricks. Floor tile came with increased prosperity along with indoor plumbing in the 1960s.

The exterior walls are 18 inches, sometimes 24 inches thick making for interesting and utilitarian window sills. Interior walls are 10-14 inches thick. All walls are considered loadbearing. Interior and exterior plaster could be 3/4 to almost 2 inches thick and using the same mud as for the bricks and mortar.

Asking about maintenance is like talking about the passing of great grandparents. The last repairs were always a long time ago. Unlike modern North American homes with weathering, paint peeling, dry rot, termites, deteriorating roofs, etc, it’s just not a concern. I’ve asked about roof leaks and everyone looked at each other like it’s a subject that’s never thought about. Finally someone will say, “We have never had a leak.”

Making adobe bricks

An adobe house can be built almost entirely from locally available materials, de la tierra—from the earth. The soil is tested by filling a large glass jar with 1/3 earth and 2/3 water. Its shaken vigorously and then allowed to sit until the water’s completely clear—one or two days. It will settle in three layers—top to bottom: clay, silt and sand, and course sand and gravel. A good mix for adobe mud is 15% clay, 10-30% silt, and 55-75% sand/gravel. Mixes will vary greatly. Up to 25% or more clay is preferred by many and there should not be too much gravel. Old builders dug the soil from favored quarries, even if it meant transporting it some distance. It was mostly dug from river banks with an abundance of clay, sand, and silt.

Adobe mud is not created by adding specific percentages of clay, sand, silt, and gravel like concrete. It comes “pre-mixed” in the soil that is selected. The mud is mixed on the construction site in a 5-inch pile spread on the ground, lower in the center. Small amounts of water are poured and uniformly mixed with a hoe eliminating lumps to create a stiff mud.

A 3-inch layer of 4-6-inch long chopped straw is spread over the mud—one part straw per five parts soil. Dead weeds, finely chopped twigs, and cow manure can be used. The fibrous material is completely worked into the mud. Once dried, abode bricks made with manure do not smell and it repels insects. The straw does not strengthen the bricks. It allows the bricks to dry evenly and quicker to reduce cracking. After the turn of the century, cement or lime was sometimes added to make them more durable and waterproof. Today liquid emulsified asphalt is used for the same reasons.

The mud is shoveled into wooden forms. Forms are not always single bricks, but multiple bricks, five or eight, for example. Bricks can be 3-5 inches thick, 8-12 inches wide, and 14-18 inches long. There is no standard size. It’s the builder’s preference. They are generally the same size for a specific house. Exterior walls may be 14-36 inches thick, usually toward the thinner. Smaller bricks might be used for interior walls though.

4 x 12 x 14-inch adobe bricks. The crude mortaring will be plastered over.

Bricks are removed from the forms after a day or two and laid on level ground to dry further. They are not stacked as the bottom ones could break. Broken bricks are okay as many half bricks are needed. Bricks are laid in the shade to dry. If sufficient shade trees are not available, leafy branches are laid over them. Drying too fast in sunlight will crack them. After a couple of days they are set on edge with an airspace between them to dry for up to six weeks. Two men can make 200-300 bricks a day. Like Rome, adobes are not built in a day. Nor can it be done in the rainy season. Once completely dry—2-3% moisture content—bricks can be stored for extended periods and stacked, but it is best to store them on edge with air spaces. They can still absorb moisture from humidly, dew, and showers.