There is something about rammed earth walls that really appeals to me. The rich colour and texture of the compacted earth links the building so well with the natural surrounds – from which the soil should ideally come. The solid bulk of the walls has an anchoring, permanent effect that connects well with the concept of ‘Sheltar’. Rammed earth has been used for millenia as a solid, durable and thermally massive.
Traditional rammed earth construction in North Africa
Rammed earth construction in modern design
It may also be surprising to you that this type of construction has been used on all continents. It was to me… I would have thought that very wet climates would not be suitable but if the walls are sealed and internal reinforcements, such as bamboo, are used, the walls can last for centuries. Reinforcing the walls is also important for areas prone to earthquakes.
Timber reinforcement to rammed earth walls
The composition of rammed earth walls are a damp mixture of earth (containing gravel, sand and clay). Lime is frequently used as a stabilizer, historically animal blood was used, and in modern times cement is often favored. In an effort to used waste as a construction material, one could also add bits of old tyres and glass to create variety and texture.
More recently, rammed earth walls are often build off of concrete foundations to provide a more durable base.
Technical diagram showing rammed earth foundation on conventional footing
So how is the wall actually constructed? Well shuttering is created using plywood or metal panels. These are clamped together a set distance apart to avoid bulging. Them the earthy mixtured is added 10 – 25mm thickness at a time, and compressed to roughly half the original height. This is what results in the lovely horizontal lines that are typical of rammed earth walls.
Rammed earth wall texture
Construction should be undertaken in the summer to maximize the warmth that assists the drying out of the walls. The curing process can take up to two years but the walls will be pretty rock hard almost as soon as the shuttering is removed.
Wall construction steps
In wet climates, the walls should be suitably covered with wide eaves or used internally, this is because over time, rain will erode the walls.
Technical detail at eaves
The process is labour intensive as each layer is physically ‘rammed’ into place. The cost though are very low and this is why it has been a favored method of construction around the world. Although it is not a strong as concrete, it achieves compressive strengths of about 4.3Mpa which is more than suitable for domestic buildings.
Rammed wall construction in progress
Rammed earth walls have a low embodied energy as almost all the material required should be sourced from the site, and unless a mechanically operated tamper is used to compress the soil, no electrical source is required.
The beautiful finish looks fantastic in modern construction, as natural as it does in very basic, traditional construction.
Contemporary design using rammed walls
In addition to the energy efficient, low-carbon construction, the thermal mass helps to regulate indoor temperature. Particularly good for hot climates as the external heat is absorbed into the thick walls and released to the cool night sky. For cold climates, insulation such as xpanded or extruded polystryrene will be good to retain warmth inside the building.
Layer of insulation in rammed wall. Good practice in colder climates.
The natural colours of the earth make for a beautiful finish
Sustainable Building Design 