Earth Building: Adobe Brick and Compressed Earth Blocks
Adobe brick building is thousands of years old. But, it’s modern too. Here are some ways to use earthen bricks to build energy efficient and sustainable homes.
Adobe construction is an ancient building method dating back to at least 7000 BC, almost 10,000 years. Earthen brick buildings can be found in the Middle East as well as the Pacific Islands and North America.
Adobe brick structures are very common here in the southwest US. The Spaniards brought the technology with them in the 1600s. Earthen buildings before that were probably made of cob.
Earth mixture to make bricks
Earth is a local and sustainable material, especially when bricks are made on the building site from the available soil. Our clay soil must be mixed with sand make good bricks. Clay alone will shrink and crack while drying, weakening the brick. Sand is added to reduce shrinking and cracking, but too much sand will make the brick crumble. Straw is sometimes added to help with shrinking and cracking.
Water is added to make a stiff mixture, but too much water, again, weakens the brick. According to New Mexico State University, the mix for strong adobe bricks is less than 30% clay, and more than 50% sand. Native soil should not have more than 30% silt.
Up to 10% emulsified asphalt can be added to further strengthen the product and make it waterproof. Commercial bricks include this as an option.
Making your own bricks
One of my neighbors built his house with bricks he made using the soil on his property. It’s time consuming and labor intensive, but the most sustainable route to take.
If you are making your own bricks, have the County Extension test your soil for its components. Then amend it to the necessary percentages. Make several mixtures and test bricks to find the right combination.
The traditional brick size is 4”x10”x14”. Forms are made of 2×4’s for single or multiple bricks. The mixture is firmly tamped into the forms and must fill out the corners well. When the brick begins to set, the forms are removed and cleaned with water to be filled again.
After three or four days, the bricks can be stood on end to cure for about a month. To save workspace, they can be stacked on an angle in ricks.
Footings need to be below the frost line, and bricks are laid in courses on a stem wall about 14” above ground level. Mortar is the same mix as that for the bricks, but with a little more water.
Bricks made in wooden forms may be uneven and not uniform. How evenly they were packed into the forms and how they dried will determine their final shape. Corners might be slightly rounded, and there may be small indentations or protrusions on the surfaces. Bricks can be sanded down to make them smoother. Mortar will have to fill in small holes, and it will be used to create a level course. The variations in the bricks will make more work.
Compressed earth blocks
Technology has removed those variations. Compressed earth blocks (CEBs) are made of a clay and sand mix similar to that of adobe bricks. Instead of being tamped into a form by hand, though, it is placed in a hydraulic presser that compresses it to a strength comparable to concrete block.
The sides of the blocks are uniformly straight, and the edges are 90º angles. There is no extra time involved to fix irregularities.
The presser is on the building site, and blocks can go from the machine to the wall. They can be dry stacked or mortared. The machine can produce enough blocks in a day for the walls of a 1000 sq ft house. CEBs are a time saver in many ways.
As always, check your local codes for building specs. Some places are more stringent than others. If you are going to make adobe bricks yourself, consult with your extension about soils, and with a contractor who has experience making and building with adobe. That will cut your experimentation time considerably.
If I was in my 30s, no doubt I’d be making bricks or blocks and building my own place!