Another alternative, instead of using sander disks, get one of those 3M paint stipper disks. They look just like a really coarse scotch brite , usually black in color. They will take the paint right of rather quickly, and do not clog like sandpaper. You can find them at any hardware store. I think that the pads themselves can be installed on on angle grinder or random orbit sanser, they attach with hook and loop on the backside.