Rammed Earth in Architecture

Rammed earth walls are meticulously crafted by compacting a precisely selected blend of aggregates, encompassing gravel, sand, silt, and a small proportion of clay, within formwork panels. In traditional practices, this involved repetitively ramming the earth mixture with the end of a wooden pole to achieve optimal compression. However, contemporary advancements have replaced the wooden pole with a mechanical ram, ushering in a new era of efficiency and precision.

For enhanced strength and durability, stabilised rammed earth presents a modified approach, incorporating a minor addition of cement typically ranging from 5% to 10%. This augmentation ensures that stabilised rammed earth walls demand minimal additional protection, although a breathable sealer is often applied to augment the material’s longevity.

Often referred to as pisé walls, derived from the French term ‘pisé de terre,’ rammed earth walls are characterized by their construction method involving the compaction of earth between two parallel frames. These frames are subsequently removed, unveiling a completed section of compressed earth wall. While walls of a minimum thickness of 500mm can still be constructed with or without cement, contemporary rammed earth walls in Australia predominantly employ cement as a stabilizer. External walls generally range from 300mm in thickness, while internal walls are typically either 300mm or 200mm thick.

Buildability, Availability and Cost

Rammed earth, an in situ construction method, utilizes readily available materials across Australia. However, the transportation of cement and formwork over long distances can lead to increased environmental and economic costs. When not employing a proprietary system, it becomes essential to conduct thorough testing of local aggregates and potential mixes.

While rammed earth exhibits favorable buildability, meticulous site and logistics planning are crucial to ensure minimal disruption to other trades within the building program. Advanced planning of services is also necessary to mitigate any potential difficulties. Following the ramming of walls in place, conduits for pipes and wires can be incorporated, similar to other masonry constructions, but this may impact surface finishes.

Opting for proprietary approaches to rammed earth construction provides the advantage of ensuring consistency and predictable performance, albeit at an additional expense. The cost of constructing a professional rammed earth building is comparable to other conventional masonry constructions of good quality. However, it can be more than twice as expensive as rendering a 200mm wide autoclaved aerated concrete block wall.

The rammed earth construction method has established a strong presence in Western Australia, where it serves as an economical option. While most states have experienced builders who comprehend its potential and limitations, the relative scarcity of this construction method outside Western Australia tends to result in higher costs. Successfully implementing rammed earth construction often entails stringent control over material sourcing and batching, as well as the utilization of costly formwork. A key factor in cost control involves designing walls as simple panels, avoiding unnecessary complexity. Although traditional rammed earth, utilizing human power for ramming and simple wooden formwork, can be cost-effective (and energy-efficient), this approach is rarely feasible in practice.