I've had some success, instead of using a bench grinder, I took my boots to a shoe repair shop and let them grind it down for me for about 10 clams. Methods differ from shop to shop so check around. I fould one old timer who used to steelhead, developed a repoire and he used to let me go in back and do it myself, then I couldn't blame him for grinding too far. Big, I mean big belt sanders with 36 grit worked the best for scuffing the sole enough for adhesion. Be careful, some may take it off too fast and then some. There's money in worm farming, but none in scab farming. Follow the directions on the packet and they have been good for a couple of years.
p.s. I usually double coat both surfaces.