I'm thinking there are other factors aside from prep that come into play. When I did mine the first time I was rushed, but the pre-bondo black looked terrible so I just wanted it done NOW. I washed the truck in a drive thru wash, dried it and applied the restore black with a sponge brush. That was Feb 2011. It lasted about a year and a half before I even started to think about doing it again. Toward the end of 2012 I did a hand wash and dry and reapplied. It still looks really good. I may do it again just for the heck of it. But considering the sod and everything else I've hauled, it surprises me how black it still is.