Rammed Earth Homebuilding

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. Building with rammed earth is a little like making adobe bricks, except the forms are larger, the earth is drier, and the bricks never moved. Sundried adobe bricks are poured into molds set on the ground, left to cure, then laid up into a wall with mortar. Rammed earth is pounded into forms set in place on the foundation. Once the form is full, it is moved to a new position along the wall.

The blocks of earth are never moved, nor is any mortar required to bind them together. The force of ramming provides the bond between adjacent sections of wall. The traditional approach to building rammed earth has been used on every continent except Antarctica and has remained essentially unchanged for 2,000 years or more. The perimeter walls of the building are defined on the ground, either by constructing some type of foundation or by marking a line in the dirt. The two form panels and two endboards are erected at some chosen starting point along the building line. Layers of moist soil are then placed into the formwork and compacted until the form is full.

Once full, it is disassembled and repositioned along the building line, one end clamped against the section just completed, the other end closed off with an endboard. This process is continued around the perimeter of the building to complete the first level (course) of wall sections. The formwork is then lifted to rest on top of the first course and the process continued around the perimeter a second time, followed by a third, a fourt—has many passes as necessary to obtain the desired wall height. Each successive circumnavigation around the building results in raising the walls approximately two feet. The higher the walls, the more difficult setting the formwork becomes and the greater the inaccuracies in plumb and line. Advances in forming technology have increased the efficiency and quality with which rammed earth walls can be built. Today, with the help of front-loading tractors, pneumatic tampers, and welldesigned formwork, earth walls can be built in a fraction of the time it used to take.

Under good conditions it is possible for a crew of four men to complete 300 square feet of wall per day, compared to the 40 or 50 square feet per day for a fourman crew working with hand tampers and baskets. The form panels we use in our work are typically 4' x 8' or 4' x 10' sheets of HDO (high-density overlay) plywood with no permanently attached supporting frame. Form ties are 3/4-inch pipe clamps spaced between 6 and 10 feet apart in the horizontal direction and 15 to 24 inches apart in the vertical direction. The distance between pipe clamps is spanned by 2" x 10" or 2" x 12" wooden planks (called walers in forming language). The walers used in forming concrete are typically 2" x 4", with ties spaced 2 feet apart. It is the extra width of the walers in our system that allows for the wide spacing of the form ties; and it is the wide spacing of the form ties that reduces the work of compacting the soil with the heavy backfill tampers.

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