I was practicing on a old hood.Sanded down to bare metal,wiped with wax and grease remover,sprayed one coat of MP 170, three coats of MP 282 primer,bc/cc.Let set 5 days.Now the problem, the paint chips to easy.The one step I did not do was sand the MP 170.If needed what grit? Oh! I forgot I also sanded the MP 282 before top-coat.What made it chip so easy?