A grinder for dry waste materials such as rubber gloves has a vertically-oriented, cylindrically-shaped housing with an opening at its upper end for receiving materials to be comminuted. The housing is divided into upper and lower chambers by means of a rotatable, disk-shaped shredder element. The shredder element has a pair of parallel upwardly-extending impeller blades disposed on its upper surface on opposite sides of its center of rotation which define a channel across the diameter of the shredder element.