Primer Holidays in 2-Stage Car Paint OK?

[SteveHGraham]

I wonder if anyone here knows anything about 2-stage automotive paint.

I finally got back to painting the side covers for one of my motorcycles. I quit a long time ago because was frustrated. I kept sanding through the primer on one cover. Yesterday I sprayed it again and sanded, and of course, I made another small hole in the primer. I brushed some primer over the hole, and I'm hoping I can sand it down to where it will work.

Question: am I going to have problems if there are areas where the primer is thin? The cover which is giving me trouble is completely covered with primer, but in some very small areas you can see the dark plastic through it. The base coat will be black, so I'm not worried about the appearance. I think the black paint will hide minor color irregularities just fine. I'm only concerned that the primer might have some minimum thickness requirement in order to get good adhesion.

[Magicniner]

If the primer is sanded thin enough to be porous you could have small areas lift but unless you have surface defects just give the whole panel a coat of a 2K self-levelling primer/surfacer, if it cures without any lifting you're good.
How did you keep sanding through? Do you not use a Guide Coat?

- Nick

[SteveHGraham]

I assume there are some irregularities in the plastic itself, and that they are trying to poke through the primer. I did use a guide coat.

[Magicniner]

Unfortunately if you didn't have the panel shape right before primer your best option is to start again, even primer-filler is not intended to replace sanding, filling and getting your shape right before going to paint, it just allows you to go to primer with a coarser surface finish.
If you have high spots you'll just keep going through until your build of primer around the high spots gets deep enough to cover them,

- Nick