For years tools like this were available at hardware stores. This type of rasp was originally designed to be used on wood, but then potters, sculptors and auto-body repairmen discovered how well the blade worked with other materials, like clay and auto-body filler. The problem with these rasps was the handle design - the handle would trap clay and get clogged. Michael designed a new open-blade shape as well as a comfortable ergonomic grip. This shredder functions well, and doesn't frustrate the user by trapping waste clay in the tool. An added benefit is the tool mark, which leaves a handsome textured surface in the clay. 

Replacement blades are available: 

Mudtools' Shredders Demo: https://www.youtube.com/watch?v=wJ_pdjCX6xg

ASSORTED COLORS, SELECTED AT RANDOM