Historically, wooden planks tied using rope were used to build walls. Formwork plays an important role in building rammed earth walls. The form must be durable and well braced, and the two opposing faces must be clamped together to prevent bulging or deformation caused by the large compressing forces. The construction of an entire wall begins with a temporary frame, the "formwork", which is usually made of wood or plywood, as a mold for the desired shape and dimensions of each section of wall. In modern rammed earth buildings, the walls are constructed on top of conventional footings or a reinforced concrete slab base. Cement-stabilised rammed earth is cured for a minimum period of 28 days. The compressive strength of rammed earth increases as it cures. 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. Old rammed-earth wall with deterioration, in FranceĪfter a wall is complete, it is sufficiently strong to immediately remove the formwork. Tamping was historically manual with a long ramming pole by hand, but modern construction systems can employ pneumatically-powered tampers.Ī typical Hmong house-building technique in the subtropical climate of Vietnam. The soil is compacted iteratively, in batches or courses, so as to gradually erect the wall up to the top of the formwork. 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. Historically, additives such as lime or animal blood were used to stabilize it. Making rammed earth involves compacting a damp mixture of subsoil that has suitable proportions of sand, gravel, clay, silt and stabilizer, if any, into a formwork (an externally supported frame or mold). The process Traditional model of construction of a wall of rammed earth on a foundation The French term "pisé de terre" or "terre pisé" was sometimes used in English for architectural uses, especially in the 19th century. The availability of suitable soil and a building design appropriate for local climatic conditions are the factors that favour its use. Įdifices formed of rammed earth are on every continent except Antarctica, in a range of environments including temperate, wet, semiarid desert, montane, and tropical regions. It has been especially used in Central Asia and Tibetan art, and sometimes in China. Under its French name of pisé it is also a material for sculptures, usually small and made in molds. It is an ancient method that has been revived recently as a sustainable building method. Rammed earth is a technique for constructing foundations, floors, and walls using compacted natural raw materials such as earth, chalk, lime, or gravel. Construction material of damp subsoil The ruins of a Han dynasty (202 BCE – 220 CE) Chinese watchtower made of rammed earth in Dunhuang, Province of Gansu, China, at the eastern end of the Silk Road.
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