This paper documents a study of concentration diffusion with complementary mechanical and electromagnetic wave measurements.  The paper starts with a review of the fundamentals of interparticle forces and wave-geomedia interaction.  Experimental data were collected during the diffusion of a high-concentration solution of potassium chloride through different soils with different boundary conditions.  Bentonite and kaolinite contracted during diffusion.  The interaction between the concentration gradient, true interparticle forces, and fabric changes produced a pore-water pressure front that advanced ahead of the concentration front.  The complex permittivity changed with the advance of the concentration front, reflecting the decrease in moisture content and the increase in conductivity.  Concentration diffusion affected shear wave propagation through changes in true interparticle forces.  Bentonite showed a significant increase in shear wave velocity, whereas the velocity of propagation in kaolinite decreased.  Published differences in the behavior of bentonite and kaolinite were compiled and hypotheses are proposed to explain observed phenomena.