Rammed earth, is a technique for constructing foundations, floors, and walls using natural raw materials such as earth, chalk, lime, or gravel.
Making rammed earth involves compacting a damp mixture of subsoil that has suitable proportions of sand, gravel, clay, and stabilizer, if any into a formwork (an externally supported frame or mold).
Historically, additives such as lime or animal blood were used to stabilize it.
Soil mix is poured into the formwork to a depth of 10 to 25 cm (4 to 10 in) and then compacted to approximately 50% of its original volume. The soil is compacted iteratively, in batches or courses, so as to gradually erect the wall up to the top of the formwork.
After a wall is complete, it is sufficiently strong to immediately remove the formwork. This is necessary if a surface texture is to be applied, e.g., by wire brushing, carving, or mold impression, because the walls become too hard to work after approximately one hour. The compressive strength of rammed earth increases as it cures. Cement stabilized rammed earth is cured for a minimum period of 28 days.
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