Stressed quartz sand saturated by water can deform by matter transport through the water phase (pressure solution). This process is modeled by a poro-visco-plastic (Voigt-type) rheology. A characteristic time constant characterizes the transition between Newtonian viscous densification and poro-plastic deformations. For short-time scales, the viscous densification is either controlled by interface kinetic or by the diffusivity of the solute Si(OH)4 at the grain contacts. For long-time scales, the poro-plastic rheology corresponds to a thermodynamic equilibrium at the grain contacts. ¿ 1999 American Geophysical Union