Earthen blocks offering alternative to steel construction

With the price of steel drastically increasing over recent months, many contractors are seeking non-traditional construction methods. In the Southwest, adobe-style structures built with earthen blocks are becoming more common.

Using blocks made out of soil is inexpensive and extremely energy efficient, according to Lawrence Jetter, owner of AECT, a San Antonio manufacturer of machines that create earth blocks. His machines, which are available in three different series, compress dirt into blocks, producing about 800 blocks an hour. Workers can take the blocks directly from the conveyor and install them immediately, using a thin layer of slurry instead of mortar between the blocks. Contractors typically own the equipment, take it to the construction site and either use dirt at the site to make the bricks or obtain dirt from another source. Jetter’s company began manufacturing the machines in 1989.

“Earth blocks have seen relative popularity, especially since the year 2000,” Jetter said. “Several universities and colleges in the Southwest are now teaching earth block construction, such as Texas A&M University’s School of Architecture.”

A professor at Southwest Texas Junior College is also researching the heating and cooling of earth blocks, Jetter continued.

Construction using earth blocks requires no internal frame or insulation. The blocks are placed on top of one another, and once cured, form an integrated structure. Anything more than two stories, however, requires additional framework. From the roof up, traditional construction methods are used. Once a wall made of earth blocks is completed, a bond beam is installed on top of the soil blocks with two steel rods running horizontally along the length of the beam. The bond beam is then placed above all load-bearing walls and connects the walls to the roof with roofing joint connectors set into the concrete.

Before the structure is finished, stucco must be applied to the earth blocks, or in areas where stucco is not readily used, the building could be covered by traditional brick. Inside, the walls can be plastered, wallpapered, or covered by wood paneling.

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According to Jetter, the blocks meet all building codes and can make the cost of construction and ownership less expensive. While the uniform building code minimums in the United States for single- and two-story structures require average block compressive strengths of 300 psi and a modulus rupture of 50 psi, compressed earth blocks generally have bearing capacities ranging from 1,100-2,200 psi with a modulus rupture ranging from 70 to 140 psi. Since workers manufacture blocks on site with available dirt, the price is also reduced, costing approximately $1.30-$1.90 per square foot of wall surface area. Jetter said no complex skills are needed to build the wall, and a four-person unskilled labor team trained by AECT can install about 1,500-2,500 blocks per day. A 1,000-square-foot house generally requires 2,700 to 3,000 blocks.

Before construction begins, the dirt to be used to make the blocks must be tested to make sure it will pass building code minimums. The soil tests are often done by AECT, or can be done at several universities, such as Texas A&M. Typically, the soil should contain 10-30 percent clay, 10-30 percent silt and 40-70 percent sharp sand. The rest can be rock under 1 inch in diameter.

Kevin Coleman, a general contractor from Uvalde, Texas, was surprised by the block’s durability and cost. He said it is superior to wood or cinder block in strength and as an insulator.

When built using double pane windows and steel insulated doors, energy savings for the owner of the building can be as much as 40 to 60 percent over traditional wood frame or concrete block construction.

“While the cost of earth brick construction is slightly less than traditional construction methods, the ownership of an earthen building is much less,” Jetter said. “A wood-frame home can cost anywhere from $320 to $360 for monthly utilities in the Southwest, but utilities for a house made of earth blocks cuts the cost down to $140 to $150 a month.”

To find out more about earth blocks, click on the link to the right.