Don't mess with all that tough and messy sanding - strip auto paint off with a chemical stripper in less than an hour.
Purchase a chemical paint stripper.
Read the directions carefully and heed all warnings and cautions.
Remove the body panel if possible and put it on a stand.
Apply the stripper liberally with a brush.
Cover the area with clear plastic. The plastic keeps the fumes in and causes the stripper to work quicker.
Wait about 20 minutes (this may vary according to the brand of stripper).
Remove the plastic and scrape the paint off with a plastic paint scraper or putty knife.
Rinse the panel with cool water to neutralize the stripper.
Sand or re-strip.
