Adobe is one of the oldest earth-based building materials used on the planet. Builders make adobe by mixing subsoil components of clay, sand, and silt and wetting the mix with water and creating a yogurt-like consistency. The adobe mixture can also include chopped straw, dung, or other organics that can help bind the block material. These additives can also allow adobe mud to shrink and dry more evenly, which helps prevents cracking. Stabilizers can also be added, including emulsified asphalt, cement, or lime to keep the adobe intact during bad weather. Adobe bricks are typically formed either by pouring a mixture into molds and allowing them to dry, or by pressing an adobe mixture with a hydraulic or manual press. The latter is commonly known as a compressed earth block.
There are no set recommended material compositions for adobe, but clay and sand (or sand with some silt and some fine gravel) are the basic components of any mixture. Clay in an adobe mixture will act as the binding material, whereas sand and other aggregates will be the inert filler that is held together by the clay. Clay typically makes up around 15-45% of any mixture, whereas sand is typically the majority material. There are no restrictions to clay and most sand types, but block makers should avoid beach sand as it contains too much salt. Adobe experts recommend the services of a geotechnical engineer who can help assess local soil sources and help create good-quality adobe recipes that meet project and safety needs.
Adobe mixtures are often molded and air-dried into bricks with stabilized blocks being cured to effective full strength after 28 days. Experts stress that the slower cure, the stronger the brick. After suitable curing or drying, builders can then use the bricks to make structural walls.
For the mold process, builders pour and press the adobe mud mixture into singular or multi open framed sections of mold forms that are set on flat ground. Builders can create or obtain mold forms made of either wood, aluminum, plastic, or steel. After initial setting, molds can be removed and the cure process can continue with bricks being turned over or handled the next day. Depending on project needs, special adobe bricks can be molded to incorporate scaffolding and reinforcement.
Compressed Earth Blocks:
Adobe mixtures can also be used to make compressed earth blocks or “CEBs”. To make compressed earth blocks, a manual or mechanical press compacts or presses the adobe mixture to form uniform and sturdy bricks. Builders commonly “stabilize” the mixes for CEBs by using a small percentage (10% or less) of cement or lime. One advantage of making CEBs compared to handmade adobe is that the process requires less time for production, as there is no drying period and there is no laying and pulling of forms. However, the process can involve noisy, heavy, and expensive machinery that will require upkeep and maintenance.
Human habitations have used earth-wall buildings for thousands of years. Wall remnants from the city of Jericho date to 8000 B.C., while some examples of earthen walls found in the Indus River Valley of India and in the Tigris and Euphrates valleys of Mesopotamia date to 7000 B.C. The Egyptians, starting around 3000 B.C., are the earliest known users of earthen bricks which included mud, concrete, and straw. The Egyptians also referenced sun-dried bricks starting around 2,000 B.C. The oldest adobe brick structure in the world, built over 5,000 years ago, is a ceremonial enclosure called Khasekhemwy at Hierakonpolis, which is in Egypt. The southwest region of the United States also has a rich history of adobe by being used by Native Americans and Spanish settlers for hundreds of years.
Starting in the 1950s, Compressed Earth Blocks were first used in South Africa and became easier to make with the development of the Cinva Ram, a manually powered and lever block making device. Compressed Earth Blocks also became popular in the United States, particularly in the southwest, beginning in the 1970s and 1980s.
Overall, cultures worldwide have used adobe for thousands of years to build homes, churches, mosques, and walls. Although many people consider or assume that adobe construction is only suitable for regions of the planet that are hot and dry, adobe homes can be built in a wide range of climates that have significant rain, moisture, and colder temperatures.
Adobes and CEBs create a high-mass wall system. They have a low thermal resistance, or R-value, meaning they have little ability to resist the transfer of heat through the bricks. A 10”-thick adobe wall will have an R-value of about 2.5 – 3.0. However, high-mass wall systems can still be energy efficient by using their thermal mass to their advantage. Adobe walls can easily store radiated heat and release it slowly, which makes it an ideal building material for desert regions where temperature fluctuations over a 24-hour period can be extreme. Adobe walls also do well in regulating humidity by soaking in moisture from the air and then releasing it back into the structure. The energy performance of high-mass walls can increase dramatically with well-designed use of insulation. Depending on the climate and building design, insulation can be placed on either side of a wall or within the middle of a double-wythe system.
Adobes and CEBs, because of their earthen material, have inherent fire resistance properties. The organization Earthbuilder’s Guild has supplied on their website a 2011 fire test assessment of an earth brick load-bearing wall assembly that achieved a fire resistance rating of 120 minutes.
Durability and Strength:
According to New Mexico architect Paul McHenry Jr., most adobe bricks have a compressive strength of 250 to 300 pounds per square inch. One major advantage of compressed earth blocks is that they have a significantly greater compressive strength of up to 2000 pounds per square inch, with the average around 1200 psi. Although mechanical compression improves the compressive strength of CEBs as compared to handmade adobe, experts who have used or studied CEBs say the addition of a cement stabilizer can double or even triple the compressive strength.
Adobe and CEB walls are just as prone to seismic damage as other unreinforced buildings made of concrete or stone. To prevent earthquake damage, walls can incorporate vertical and horizontal reinforced blocks, concrete channels, and anchorage to bond beams.
Adobe and CEB have favorable acoustical benefits in isolating and reducing noise. A 2014 University of Oklahoma study shows that a compressed earth block wall provided almost twice the sound loss when compared to a wood framed wall, without compromising sirens and other audible alerts.
In colder climate zones, all buildings will experience freeze/thaw cycles. Adobe bricks and CEBs can be damaged by excessive moisture entering the wall system, and by water freezing inside the assembly. With proper exterior detailing and design, much of this potential damage can be mitigated.
Although many experienced builders prefer to construct load-bearing walls with adobe, adobe bricks can be conducive to both stick framing and post-and-beam framing that can be the primary load-bearing components of an adobe house. Regardless of any type of wall or load-bearing structure, builders must take special care and attention to ensure strength and stability, including employing the help of an architect and structural engineer who will help comply with local building codes.
As of 2022, the following are three major code sources applicable to adobe masonry within the United States:
The International Building Code (2021) – Building codes for earthen masonry are set forth in the IBC Chapter 21 – Section 2109 – Empirical Design of Adobe Masonry
The ASTM E2392 (2016) – Standard guide for the design of earthen wall building systems.
14.7.4 NMAC New Mexico Earthen building materials code (2015 updated)
For building permits, experts say it is important for owner-builders to check in with their local building officials to find out what codes are applicable to the project and what steps will be necessary for an engineering team to certify a project.
It is possible to leave adobe and CEBs exposed, but many adobe builders apply earthen plasters to the walls enabling them to have an intact, protective, smooth, and clean finish with no dust.
Owner-builders can perform a jar test to determine if subsoil from a site is suitable for making adobe. This involves digging a hole two to three feet deep to make sure the owner-builder tests subsoil rather than the organic material of topsoil. Subsoil from the hole should be mixed to combine all potential layers. The owner-builder should then place a portion of the mixed soil into a quart size jar with three to four inches of water added on top. Next, the owner-builder should shake the contents of the jar vigorously and then place it on an even surface to assess the contents as they settle. As the contents settle, the owner-builder can then mark the clay layer and the aggregate layers against the entire mixture for their percentages. If the mixture is more than 45 percent of clay, the owner builder will likely have to add extra sand to the eventual mixture that comes from the soil of the site. If the self-test shows too little clay, the owner-builder will then need to purchase or get suitable soil or clay from another source. Experts recommend hiring a soil-stabilization engineer to carry out testing and to provide a mix formula suitable to meet project, code, and safety needs.
A 2,000 square foot home will have approximately 2,315 square feet of adobe walls and will require roughly 5,120 adobe bricks. Wall thickness and window placement of solar passivity are factors that can increase or decrease the number of bricks necessary for a project. A calculation used to quantify bricks involves measuring the total square footage of the walls (excluding openings) and subtracting the overlap of wall intersections and multiplying the total by 2.2 if using feet. Experts recommend making more bricks than estimated to address any deficiencies in design or calculations.
Adobe Architecture, A Simple Guide with Plans for Building with Earth by Myrtle and Wilfred Stedman, Sunstone Press, 8th Edition, 2016.
Adobe Homes for All Climates: Simple, Affordable, and Earthquake-Resistant Natural Building Techniques by Lisa Schroder and Vince Ogletree, Chelsea Green Publishing, 2010.
Earthbuilders Encyclopedia: The Master Alphabetical Reference for Adobe and Rammed Earth by Joe Tibbets, Southwest Solaradobe School, 1989.
Adobe and Rammed Earth Buildings: Design and Construction by Paul Graham McHenry, Jr., University of Arizona Press, 1989.
Adobe: Build It Yourself by Paul Graham McHenry Jr., University of Arizona Press, Revised Edition, 1985.
The Owner-Built Adobe House by Duane Newcomb, University of New Mexico Press, 2001.
The Earthbuilders’ Guild – Alameda, NM
The Earthen Construction Initiative – San Antonio, TX
Adobe In Action – Silver City, NM
The Adobe Alliance – Santa Fe, NM
Endeavour Sustainable Building School – Peterborough, OT