Rammed earth, also known as tapial (Spanish), and pise (de terre) (French), is a technique for building walls using the raw materials of earth, chalk, lime and gravel. It is an ancient building method that has seen a revival in recent years as people seek more sustainable building materials and natural building methods. Rammed-earth walls are simple to construct, noncombustible, thermally massive, strong, and durable. They can be labour-intensive to construct without machinery (powered tampers), however, and they are susceptible to water damage if inadequately protected or maintained. Rammed-earth buildings are found on every continent except Antarctica, in a range of environments that includes the temperate and wet regions of northern Europe, semiarid deserts, mountain areas and the tropics. The availability of useful soil and a building design appropriate for local climatic conditions are the factors that favour its use.
Building a rammed-earth wall involves compressing a damp mixture of earth that has suitable proportions of sand, gravel and clay (sometimes with an added stabilizer) into an externally supported frame or mould, creating either a solid wall of earth or individual blocks.
The construction of an entire wall begins with a temporary frame (formwork), usually made of wood or plywood, to act as a mould for the desired shape and dimensions of each wall section. The form must be sturdy and well braced, and the two opposing wall faces clamped together, to prevent bulging or deformation from the large compression forces involved. Damp material is poured in to a depth of 10 to 25 cm (4 to 10 in) and then compacted to around 50% of its original height.