How fine do you sand your cars before paint? Same for enamel, urethane, single stage, clear coat? Just as I thought I was getting close to booth time my pal came over and said I'd better get all those sand scratches from the bodywork cleaned up. Disheartening, but he is right of course. A year or two ago I painted my work truck single stage white urethane and was surprised how much sand scratches showed up. He said in the Centari days it flowed more and would fill more imperfections than urethane, which tacks up quicker. Seems to be the case from what I remember. I'll be using single stage urethane again most likely, and have it sanded with 320 now. Good enough? What about sand scratch swell, is that a thing of the past with today's urethane primers and topcoats?