I have some serious scuffing on my car’s door sill. I bought some black xpel film to prevent this in the future, but I want to do something to prevent rust from forming underneath the film.
I bought some color matched touch up paint, but I’m wondering if I need to remove all of the paint and primer from the area. Since I don’t care how it’ll look under the film, I’d like to just rough it up with sandpaper, prime and paint it, and then slap the film on it.
The part I’m worried about is that it’s a fairly large and irregular scuffed area. Some bits are down to metal, some down to primer, and some still has the clearcoat. I can’t really mask it off and only get primer on bare metal and the original primer.
The reason I don’t want to sand it all down is that it’s a difficult area to sand. I’m worried I’ll fuck up the paint beyond the area that would be covered by the film.
Can I do it the lazy way, or should I just bite the bullet and sand down to metal?
It’s water based touch up paint if that matters.
I forgot to focus on the rust part of your question.
Preventing rust from scratches is the original primer’s job. If it is fully scratched through to metal and you only care about preventing rust there’s basically two options I am aware of. The first is to refinish the panel or do an expert job at spot repair (allegedly very difficult), beginning with heavy sanding to identify where the scratches are and ideally remove them so they so not remain nuclei for rust. The other is to clean and adopt a protection routine to slow down any rusting process. Basically apply some mild anti-rust, wash thoroughly with water to remove electrolytes, dry immediately and thoroughly, perhaps with rubbing alcohol, and then wax. Consistently waxing every two weeks or so creates a protective barrier. There are easy spray on + buff waxes out there if you want to do it in just that spot.
Monitor the paint for bubbling, which indicates a deep and pervasive rust and a need to replace the entire panel.