Published: 01/10/2019 By Allan Fuller
The cheapest and most sustainable building material available in the world.
With the environment increasingly the focus of attention it is easy to find what are considered the obvious polluters. Truth is however that there are a myriad of other polluters that are disregarded. Modern building construction should take its share of the blame. With raw materials that may have traveled the globe to get to their destination and as we have pointed out before the work running out of building sand it is perhaps time to look at history and traditional methods.Rammed earth, also known as taipa in Portuguese, tapial or tapia in Spanish, pisé de terre in French, and hangtu in China is ideal for foundations, floors, and walls using natural raw materials such as earth, chalk, lime, or gravel. It is an ancient method used that has been revived recently as a sustainable building material used in a technique of natural building.
Rammed earth is simple to manufacture, non-combustible, thermally massive, strong, and durable. However, structures such as walls can be laborious to construct of rammed earth without machinery, e. g., powered tampers, and they are susceptible to water damage if inadequately protected or maintained.
The construction of an entire wall begins with a temporary frame, denominated the "formwork", which is usually made of wood or plywood, as a mold for the desired shape and dimensions of each section of wall. 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. Damp material 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 height. The material is compressed iteratively, in batches or courses, so as to gradually erect the wall up to the top of the formwork. Tamping was historically manual with a long ramming pole, and was very laborious, but modern construction can be made less so by employing pneumatically powered tampers.
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. Construction is optimally done in warm weather so that the walls can dry and harden. The compression strength of the rammed earth increases as it cures; some time is necessary for it to dry and as long as two years can be necessary for complete curing. Exposed walls must be sealed to prevent water damage.
Where blocks made of rammed earth are used, they are generally stacked like regular blocks and 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 material into blocks.
Presently more than 30% of the world's population uses earth as a building material. Rammed earth has been used globally in a wide range of climatic conditions. Rammed-earth housing may resolve homelessness caused by otherwise expensive construction techniques.
The United States Department of Agriculture observed in 1925 that rammed-earth structures endure indefinitely and can be constructed for less than two-thirds of the cost of standard frame houses.