The hydrodynamics and statics of wet colloidal systems depend on the solution salt type and solution concentrations with which they are in equilibrium. The management of these systems therefore requires some understanding of the consequences of hydrodynamic dispersion and chemical reaction that may accompany non-steady water Bow in these systems. Experimental data indicate that calcium invades, reacts with, and causes structural change in the clay when an initially uniform wet slurry of sodium bentonite is subject to constant pressure filtration in which a very thin and permeable disc of CaSO4 acts as the filter membrane. A model is proposed which permits systematic examination of the phenomenon. The experiments and the model offer rational methods for examination of the basic physical chemistry and its physical consequences and also of analogous and practically important cases in management of filtration, of slip casting and the use of clay liners to retention ponds containing noxious and toxic effluents.