Rammed earth is an ancient method of construction in which soil is compressed to create attractive and durable walls and floors with earth-toned striations. While this technique has long been used around the world to build structures as impressive as the Great Wall of China, it has only recently been revived in the U.S. as an environmentally friendly and potentially lower cost alternative to concrete.
This method uses forms in which a mixture containing earth, sand, clay, lime, or other binders are placed in layers. Pressure is then applied to create a hard and durable surface similar to sandstone. The technique can be used to form rammed earth walls and floors, as well as bricks and blocks. This construction method offers many green building benefits, including low embodied energy, high recyclability, and non-toxicity. As rammed earth has high thermal mass, the walls absorb the sun’s heat during the day and then slowly release the warmth at night.
Contemporary manufacturers of rammed earth building material often add small amounts of cement to increase the strength, as well as silicate-based waterproofing agents for construction in colder, wetter climates. Researchers at University of British Columbia Okanagan recently reported having tested the addition of calcium carbide residue and fly ash as binding agents in rammed earth. They found that when cured, the walls containing these binding agents were 25 times stronger than those without, making them more suitable for modern construction.
A number of builders in the U.S. employ this method by pouring walls onsite or creating customized rammed earth panels. Among the rammed earth building products on the U.S. market are blocks manufactured by California-based Watershed Materials. The blocks, which incorporate locally sourced, unwashed aggregate and have low cement content, are a lower carbon alternative to concrete blocks that can be installed by any mason.