earth building worldwide is concentrated in Australia, France, Arizona, New Mexico and California. Compared to other earthen materials like adobe, rammed earth has greater crush strength and is much more resistant to erosion. As Daniel Chiras (2000) points out, the rocklike character of the cured rammed earth wall basically results from its replicating the process of sedimentary rock formation, but in a much shorter time span. Its thick variously coloured walls are attractive and can be built in a variety of regional and architectural styles. Any number of roof systems can be employed with them. Rammed earth is amenable to energy-efficient design, and provides lots of thermal mass, which is desirable for passive solar design. Unlike wood buildings, rammed earth buildings are termite and pest resistant, and defy earthquakes, tornadoes and hurricanes. They resist decay and are extremely durable. Fire actually hardens and strengthens rammed earth walls; and they are virtually soundproof. A drawback of rammed earth, compared with other natural building systems, is that it can be exacting and cumbersome, and is probably best carried on by professional contractors. A crucial factor is the right soil mix, strong on mineral matter, with an absolute minimum of organic material. The ideal mix consists of about 70 percent sand and aggregate, and 30 percent clay which acts as the binder. The clay, however, has to be just the right kindwhich is non-expansive; and in cold or wet climates, a certain amount of Portland cement is required to increase strength and water-resistance. While rammed earth makes good use of local materials, just any soil is not acceptable. Prospective soils must first be tested, and if necessary augmented by, e.g., road base or