Wet sand with 400 grit paper until roughness is gone, then follow the advice of Richard L. You should have a very slick job after that. BE CAREFUL YOU DON'T WANT TO LET THE SPRAY CAN GET TOO HOT!! yOU DON'T NEED IT TO RUPTURE AND CAUSE HARM. Just good warm water and dry water on spray nozzle before spraying so it won't contaminate the paint.