Campy has it right. Just besure to keep it good a wet. I will actually keep a small bucket next to the work area with water in it and keep a couple of pieces of sand paper soaking. Sand a little with one piece and rinse it in the bucket and get another piece that's been soaking. Sand with it for awhile and repeat the process getting the piece before. I also use a spray bottle to keep the surface wet. Sand lightly!