Clay

The fine fraction of the soil mix that gives earthen construction its cohesive binder. Saharan-Maghreb soils used in pisé and adobe are typically a graded mix of clay, silt, sand, and gravel; the clay fraction provides plasticity during shaping and binds the inert aggregate during drying. Clay content that is too high produces excessive shrinkage cracking; too low, insufficient cohesion. Maalems traditionally evaluated suitability through tactile and visual tests of the local soil rather than by formal mineralogical analysis, and one reason for the regional variation in pisé technique is the variation in the parent geology of available borrow pits.