The effect on clays and the stabilizing effect of damp clays on ungraded natural aggregates germinated an idea upon which a mortar theory for bituminous mixes might be based. This mortar theory, stated briefly, is the formation of thin films of bituminous binder upon the minute particles of a mineral dust to form a bituminous mortar, and the mortar so prepared to be used to bond aggregates together into a bituminous mixture suitable for paving purposes. In order to test the validity of the mortar theory as quickly as possible, known methods of producing such thin films were studied and the impact process selected for this purpose in further tests.