Silt, clay, soil are natural building materials and occur in different compositions under the top mold in every part of the world. Silt is made up of clay and sand and develops out of the destruction of other native rock. Hardly any silt is the same. The sand and clay parts are just as important as the clay kind for its building characteristics. Silt soils often show the complete spectrum of soil colors: from white to light beige, yellow to ochre, brown to gray blue and red. In its damp condition, silt is according to its composition, a more or less ductile material which becomes load-bearing through air drying. More than a third of the world's population lives in houses, which have been built completely or at least to some part in silt and rammed earth. Up to 40 different earthen building techniques have been used. Just as different the local silt and soil compositions are, so are the according earthen building techniques.