Washing processes are characterized by the replacement of the initial liquids by another liquid (the wash liquid). In the paper being presented, the experimental studies have been conducted in lab sedimentation equipment. It was exhibited an increment in the porosity of the moving bed with the average vertical velocity at a fixed width of the wash chamber. The experimental results show that the porosity values in the moving bed for both fractions of sand are slightly higher than the values of the moving bed with viscosity ratio (η∗) equal to one. The differences are in the range of 3-5 % at the chosen conditions.