I use industrial wet/dry sandpaper on a granite surface plate. I do it in the sink with a small trickle of water running over the stone and paper. I do the grid thing forst to be sure the entire surface has been touched and is flat and use laerge and small varying figure eight patterns. I am lapping natural stones, the Thuringian Water Hones I sell and have no problem with grit sticking in these stones. I tested a random sample 2x8 stone I lapped and it was flat within .0006 using this method.

Tony