Rammed Earth Homebuilding

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For our work in the United States, we always use mechanical tamping equipment, powered by compressed air. The hand tampers are only used in tight spaces and around the plumbing fitting and electrical boxes. On a large project, we'll have four to six 30-pound pneumatic rammers in operation, all hosed to a 120 cubic feet per minute (cfm) air compressor.

The compaction process begins at the bottom of the form box, on a four- to sixinch layer of prepared soil mix. When tamping by hand, stand in the form box and first settle the soil with your feet. Lift the tamper about 12 to 18 inches high and let it drop. Begin at one end of the form and work your way along from side to side.

Two or more people in the form—as many as can fit comfortably, in fact—will improve the rate of production. The rhythm of a team effort yields a psychological boost to the work. Lift and drop. Lift and drop. As the soil becomes compacted, the sound of the tamping will change from a dull thud to a ringing sound. When the layer rings, it's time for more earth.

Once a soil layer has been completely compacted, shovel in another four to six inches and repeat the tamping ritual. Place layer upon layer until the form is full and the top layer is hard. Because each of the layers benefits from the forces applied to it by the ramming of the layer above, you'll need to take twice as much time compacting the top layer as you did the others.

The above procedure for building a wall section, as you might guess, results in a "layered" look. Once the forms are stripped, the wall will display very visible horizontal lines between each of the courses, like sedimentary rock. The more level and consistent each of the loose courses are, the more uniform the layers in the finished wall. This layering is the traditional look of rammed earth. If desired, it can even be accentuated by increasing the thickness of each layer, from six inches of loose material to eight.

Whatever method of ramming you choose to use for your projects—buckets and hand tampers, thick layers and pneumatics, or continuous delivery—the results are structurally the same. If the soil has been selected carefully, moistened properly, and well compacted within the formwork, rammed earth walls become like stone. Believe it or not, like stone, the home becomes stronger with age ...which will be a comforting fact to your greatgreatgrandchildren as they stoke up the fire in the home you built so long ago.

The above article was adapted from: The Rammed Earth House (Chelsea Green, 1996) by David Easton. Copyright © 1996 by David Easton. David's comprehensive guide is available for $30.00 through MOTHERS Bookshelf (see pages 88 and 89) by calling 1-800-888-9098 and asking for product number MEB234.

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