Just got the car back from media blasting. Car is very clean, but needs a lot of metal work. My question is it better to go ahead and primer it first, or just let it get some rust, do the metal work, and Ospho it and primer later?
I think you should primer it... that way you avoid the reasoning for the media blasting in the first place, and any place that chips/cracks/etc the primer can just be re primered and then blocked down for paint
you want to lay down a good etching primer first, then do your metal work. the primer will allow better guide coats, and it will also allow any body filler you use to stick better than it would to bare metal, unless you are going to use lead. cover over that with a good primer-sealer if you are not going to paint right away to prevent moisture from getting behind the primer and causing rust. remember that primers, except primer-sealer, are porus and will let moisture in.
the way my car was done,we got the car down to the metal and every
day after they were done working on the car they would cover it and keep it
inside there shop,away from moisture and try not to touch the car all over the place once the metal work is done then you can primer it but make sure you use a primer that will protect the bare metal from rust.
after that primer is on you use a body filling primer and get a guide coat on there so it's easyer to block you car.
Check out www.hotrodders.com body shop board. Most of they guys there (many professional) recommend an epoxy primer immediately after sandblasting and then go from there. Lot's of good info there.
I'm in the process of having my 69 stripped and painted. To save money (and to be sure that it's done right) I volunteered to strip the door/hood/trunk jams myself. The paint shop requested I lightly prime the bare metal with a zinc self etching primer.
Another vote for epoxy primer. Most epoxy primers allow you to put polyester filler over the top, which an etching primer won't. I have used both and do like the characteristics of etching primer, but would personnally go with an epoxy. I absolutely would not wait if you are in a high humidity area or you will be blasting twice.