How long can primer be left without top coating? I need to do some rust repair on my 1995 F150 but plan on doing it in stages over the next 6-12 months. What primer would hold up best for this type of schedule.

 

Epoxy primer. You can leave it for years. They way that I do it is use it for a base over the metal after you've done your metal work. Then do your bondo and high fill primer and block it out. After you're happy with it top it with another coat of epoxy. You can also do your metal work, hit it with epoxy then come back later with bondo / high fill. If it's more than 5 days or so you need to scuff it and shoot another coat before painting anything else over it.

Southern Polyurethanes Home - Here's the stuff I use now. Their black primer has a UV inhibitor in it to last longer because so many people use it as a top coat. I used to use PPG Omni.

They also have a forum for all your paint questions.

As for high fill, lots of people like 2k, but I prefer a 1k. It doesn't dry as fast but they both build nice and the 1k lasts longer on the shelf. For a production shop I'd use 2k but for home and project use 1k. Just my preference.

 

I would agree Epoxy is the only primer to use if you plan on it sitting. I would go over that with a 2k after the body work, Epoxy is really hard to sand and has a low film build. A note tho with Epoxy you can't use any type of acid etch and make sure the metal is very clean before application. Epoxy is more sensitive to clean prep work

 

I have used 2 stage epoxy primers (primer & hardner= 2 stage) in my body shop since they became available years and years ago.It sands EASILY and will withstand not being topcoated for a long period of time as opposed to single stage primer which is succeptable to attracting moisture as it sits. Do not go cheap on this layer as all the other coats of whatever are only as good as the weakest link. Good luck!