Abstract: Apparatus is disclosed for removing material from the surface of a solid substrate. A rotary cutter cage is mounted on a support frame and has at least one row of a plurality of cutters mounted on a bar connected to the cutter cage. The cutters impact a solid substrate during rotation of the cutter cage. Each cutter has a bore through which the bar extends in mounting the plurality of cutters on the cutter cage. The bore is larger than the bar to permit rotation of each cutter on the bar at least during contact with the surface being treated. A brake is provided on the cutter cage to brake rotation of the cutters after each occurrence of a corresponding row of cutters contacting the surface being treated during rotation of the cutter cage.