Question

Rammed-earth and adobe walls are sometimes used in the southwestern and south-central United States, among other places worldwide. The selection of one system over the other might be made based on the character of the native soil. What is the fundamental difference between the soils used in rammed earth and in adobe walls?

Answer

Adobe walls are typically made from soils high in clay. These clay soils are mixed with straw, which acts as a binder, and then pressed into forms to dry into large bricks. Rammed earth, on the other hand, uses soils low in clay. Damp non-clay soil free of organic matter is often mixed with a small percentage of cement and compacted between forms to create a monolithic wall section. In southern France this wall system is called pisé (or pisé de terre).