Adobe

Adobe is one of the oldest building materials in use. It is basically just dirt that has been moistened with water, sometimes with chopped straw or other fibers added for strength, and then allowed to dry in the desired shape. Commonly adobe is shaped into uniform blocks that can be stacked like bricks to form walls, but it can also be simply piled up over time to create a structure. The best adobe soil will have between 15% and 30% clay in it to bind the material together, with the rest being mostly sand or larger aggregate. Too much clay will shrink and crack excessively; too little will allow fragmentation. Sometimes adobe is stabilized with a small amount of cement or asphalt emulsion added to keep it intact where it will be subject to excessive weather. Adobe blocks can be formed either by pouring it into molds and allowing it to dry, or it can pressed into blocks with a hydraulic or leverage press. Adobe can also be used for floors that have resilience and beauty, colored with a thin slip of clay and polished with natural oil.

Adobe buildings that have substantial eaves to protect the walls and foundations to keep the adobe off the ground will require less maintenance than if the walls are left unprotected. Some adobe buildings have been plastered with Portland cement on the outside in an attempt to protect the adobe, but this practice has led to failures when moisture finds a way through a crack in the cement and then can't readily evaporate. When adobe is used as an exterior plaster it is either stabilized or replastered on a regular basis.

Adobe is a good thermal mass material, holding heat and cool well. It does not insulate very well, so walls made of adobe need some means of providing insulation to maintain comfort in the building. Sometimes this is accomplished by creating a double wall, with an air space, or some other insulation in between. Another approach is placing insulating materials on the outside.