RAMMED EARTH BUILDING
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.
The material is compressed iteratively, in batches, gradually building the wall up to the top of the frame. Tamping was historically done by hand with a long ramming pole, and was very labour-intensive; modern construction can be made less labour-intensive by employing pneumatically powered tampers. Once a wall is complete, it is strong enough for the frames to be immediately removed. This is in fact necessary if a surface texture is to be applied (e.g., by wire-brushing, carving, or mould impression), since the walls become too hard to work after about an hour. Construction is best done in warm weather so that the walls can dry and harden. The compression strength of the rammed earth increases as it cures; it takes some time to dry out, as much as two years for complete curing. Exposed walls should be sealed to prevent water damage.
In modern variations of the method, rammed-earth walls are constructed on top of conventional footings or a reinforced concrete slab base.
Where blocks made of rammed earth are used, they are generally stacked like regular blocks but are bonded together with a thin mud slurry instead of cement. Special machines, usually powered by small engines and often portable, are used to compress the earth into blocks. Today, as more people recognise the practical and aesthetic benefits of this ancient building technique, Rammed Earth Construction has moved into a much broader market.
Work is increasingly being carried out in the suburbs, as well as eco-friendly bush retreats and more recently commercial projects that understand the benefits of building in a environmentally sensitive manner.