For pisé construction, earth must be dry enough for the shuttering to be lifted directly after ramming without damaging the wall. Shrinkage needs to be as little as possible to avoid cracks. A well-graded earth with about 12% clay is best. An earth mixture with up to 30% clay is usable, but will be harder to form. Sand can be mixed with earth that has too much clay, and clay can be added to earth that has too little.
For adobe blocks a much more fatty earth with up to 40% clay (or even more in blocks mixed with straw) can be used.
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