I have a body shop in NC we do lots of custom work and have used it all threw the years but I love nason 421-17 primer and have had lots of years with it and no problems, I have tried slick sand and like it but be sure to epoxy any bare spots I had some that would not dry one time and it was over bare steel anouther shop in the area had the same problem and never found out why.I was scared of all that film build here in NC because its so hot in the summer and very cold in the winter thought it may cause problems over the years.