The mixture {x(C12H27CO2)(2)Pb + (1 - x)C12H27CO2H} has been investigated by differential scanning calorimetry and hot-stage polarizing-light microscopy over the whole composition range. Molecular association between the acid and the salt typical of the systems with alkaline cations is not found in the solid state. The complete phase diagram resembles those of the surfactants in water with a Krafft-like effect pointing to the formation of micellar aggregates and lyotropic phases.