Rammed earth is a sustainable building technique that’s been around since man discovered that by combining earth, chalk, lime and gravel, pouring it into a mold and pounding it down, he could create walls, houses and fortifications. Ironically, I’m using this ancient construction process to build a series of walls, seating areas and terraces in a garden I’m doing for the one of the stars of the most successful SciFi program currently on network television.
As described in Wikipedia, Rammed earth, also known as taipa (Portuguese), tapial (Spanish), and pisé (de terre) (French), 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, incombustible, thermally massive, strong, and durable. They can be labor-intensive to construct without machinery (powered tampers), 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 favor its use.
Building With Rammed Earth
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 mold, creating either a solid wall of earth or individual blocks. 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.
Historically, such additives as lime or animal blood were used to stabilize the material, while modern construction uses lime, cement or asphalt emulsions. Some modern builders also add colored oxides or other items, such as bottles or pieces of timber, to add variety to the structure.
Creating A Temporary Framework
The construction of an entire wall begins with a temporary frame (formwork), usually made of wood or plywood, to act as a mold 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 labor-intensive; modern construction can be made more efficient by employing pneumatically powered tampers.
Once a wall is complete, it is strong enough that the frames can be removed immediately. This is necessary if a surface texture will be applied (e.g. by wire-brushing), 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.
Go Native And Help Save Our Planet
If you’re considering adding hardscapes to your garden (terraces, steps, walkways, retaining walls) you should seriously consider building with rammed earth. It’s beautiful, sustainable and extremely earth friendly.