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Compressed Earth Block often referred to simply as CEB, is a type of manufactured construction material formed in a mechanical press that forms an appropriate mix of dirt, non-expansive clay, and an aggregate into a compressed block. Creating CEBs differs from rammed earth in that the latter uses a larger formwork into which earth is poured and tamped down, creating larger forms such as a whole wall or more at one time. CEB blocks are installed onto the wall by hand and a slurry made of a soupy version of the same dirt/clay mix, sans aggregate, is spread or brushed very thinly between the blocks for bonding. There is no use of mortar in the traditional sense. (This is not necessarily true for vertical presses, see link at bottom of page)

The advance of CEB into the construction industry has been driven by manufacturers of the mechanical presses, a small group of eco-friendly contractors and by cultural acceptance of the medium in areas where it is seen as superior to adobe. In the United States, most general contractors building with CEB are in the Southwestern states: New Mexico, Colorado, Arizona, California, and to a lesser extent in Texas. However, manufacturers of the mechanical presses enjoy their heaviest sales overseas. Mexico and Third World countries have been attractive markets for the presses for years.

The advantages of CEB are in the wait time for material, the elimination of shipping cost, the low moisture content, and the uniformity of the block thereby minimizing, if not eliminating the use of mortar and decreasing both the labor and materials costs.

· CEB can be pressed from humid earth. Because it is not wet, the drying time is much shorter. Some soil conditions permit the blocks to go straight from the press onto the wall. A single mechanical press can produce from 800 to over 5,000 blocks per day, enough to build a 1,200 square feet (110 m2) house in one day.

· Shipping cost: Suitable soils are often available at or near the construction site. Adobe and CEB are of similar weight, but distance from a source supply gives CEB an advantage. Also, CEB can be made available in places where adobe manufacturing operations are non-existent.

· Uniformity: CEB can be manufactured to a predictable size and has true flat sides and 90-degree angle edges. This makes design and costing easier. This also provides the contractor the option of making the exteriors look like conventional stucco houses.

CEB had very limited use prior to the 1980s. It was known in the 1950s in South America, where the Cinva Ram was developed by Raul Ramirez in the Inter-American Housing Center (CINVA) in Bogota, Colombia. The Cinva Ram is a lever-action, manual press that makes one block at a time.

U.S. manufacturers produce much larger machines that run with diesel or gasoline engines and hydraulic presses that receive the soil/aggregate mixture through a hopper. This is fed into a chamber to create a block that is then ejected onto a conveyor.

During the 1980s, soil-pressing technology became widespread. France, England, Germany and Switzerland began to write standards. The Peace Corps, USAID, Habitat for Humanity and other programs began to implement it into housing projects.

Construction method is simple. Less skilled labor is required; wall construction can be done with unskilled labor encouraging self-sufficiency and community involvement. If the blocks are stabilized with cement and/or fly ash, they can be used as bricks and assembled using standard masonry techniques of brick-laying.

Soil mix conditions: The soil mix is 15-40 percent non-expansive clay, 25-40 percent silt powder, and sharp sand to small gravel content of 40-70 percent. The more modern machines do not require aggregate (rock) to make a strong soil block for most applications. Soil moisture content ranges from 4 to 12 percent by weight. Clay with a plasticity index (PI) of up to 25 or 30 would be acceptable for most applications. The PI of the mixed soil (clay, silt and sand/gravel combined) should not exceed 12 to 15; that is the difference between the Upper and Lower Atterburg Limits, as determined by laboratory testing.

FACT: Earthen construction, as incorporated in UDC projects was first used by the

ancient Sumerians in urban design more than 6,000 years ago it was is now present

day Iraq.

FACT: Passive design and orientation was again first utilized by the ancient Sumerians, but fully realized and successfully integrated into building design as a essential design feature by civilizations such as the Egyptians, Romans, Greeks Mayans, Incas, Aztecs and American Indian tribes of the Southwestern United States.

FACT: Taos Pueblo constructed between 1000 and 1045 A.D. is the oldest continuously inhabited house in the United states. The home incorporates both earthen building techniques and materials as well as passive polar orientation strategies to achieve efficiency and performance.

FACT: More than one half of the world's population,

 approximately 3.5 billion on six continents, live and

 work in earth buildings.

FACT: The oldest known earth building in the world

 that is still standing and used is a Mosque in

Djenne, Mali (Right). Constructed entirely of rammed earth

and coated in a festival annually with a natural

mud plaster for over 1,100 years. The Mosque is

7 stories high.

FACT: UDC projects such as the Universal Home™ and shelter design use natural Lime plaster. The plaster is applied to the interior and exterior of the wall systems. The plaster is made up of Nopal cactus as a binder of Lime and clay elements i to create a exterior semi-permeable membrane. A techniques that is thousands of years old, but still widely utilized through out the world.

ABOVE: A hybrid CEB/ Light Frame constructed home in South Texas consists of an exterior 14” CEB wall system capable of shielding the home from thermal gain during the day.

ABOVE: A Construction worker manufacturers CEB’s using a AECT 3500 Series Pressing Machine. The machine is capable of producing 5,500 Blocks pure day.

ABOVE: A standard size pallet of CEB’s consisting of 72 10” x 14” x 4” blocks weighing in at 2,500 pounds.

ABOVE: A Construction worker lay CEB’s using the wet stack method. Each block is compressed at over 2,700 PSI by hydraulic presses and void of 95% of moisture. Each block has a compressive strength of 1,000 PSI.

ABOVE: The LMI-1 Universal Home™ constructed in abilene, Texas consists of 14” exterior CEB wall system and a 8” CEB interior wall system.

BELOW: Nopal cactus, indigenous to much of the South Western United States serves as a primary component in natural Lime plaster used to overlay the CEB’s. BELOW LEFT: Student Volunteers cut Nopal cactus into 1” squares to be used to produce cactus water, a natural binder. BELOW RIGHT: Construction workers install Natural Lime Plaster in two coats; Scratch Coat (Red) and Finish Coat (White).