If the spots are small, no bigger than a nickel, I'd just go ahead and paint it. It's not going to come off or anything like that. If you don't believe it just spray some paint on a clean piece of glass and see how well it sticks.

However, if the sanded through areas are large it probably means that the surrounding area is low and needs filler or you didn't use enough primer, but only you can make that determination.

Points to consider:

Epoxy primer is best over bare metal because it is not porous and therefore will prevent rust. It should be used if you want a protective coating over bare metal for an extended period of time. There is no other real legitimate reason to use it unless you want to make a chemistry project out of painting your vehicle.

High Fill primer is perfectly fine over bare metal as long as you protect the vehicle from rain. It can also be applied over any material that will not react with it as long as that surface is sanded and since it fills sanding scratches you can scuff the surface with 80-grit for an aggressive tooth.

Surface preparation and block sanding is a skilled and highly respected craft that is perfected over years of practice, but the novice can also produce an excellent finish with today's technology and an understanding of block sanding which is another subject far beyond the scope of this response.

Woody
Your Brother in Bolthood

My 1951 half-ton 'Ol Red

Save the VINTAGE DOOR ART! Please contribute photos.
Door Art Collection