I've been using cheapo lacquer primers to build with. I usually shoot epoxy over bare or filler, then build and sand with the lacquer. I got the sand scratches in some fenders after doing the same process same primer, same sandpaper grits on the hood that turned out beautiful.
But as I think back, I let the hood sit in final primer coat for a couple of days before I finished sanding. Also, my temps were around 80 deg. I probably ought to give the primer layers some time to cure? Maybe also stop using lacquer primer?
Joined: Apr 21, Posts: 1, Profile Page. Joined: Apr 3, Posts: Profile Page. Yeah always use a high build primer that has a catalyzed hardener. I know it's more money but it's definitely worth it.
You can fill in 80 grit scratches with it. Saves alot of time. I've read articles where the old time pros used to leave lacquer primer sit for sometimes up to six months. It's just not worth going through all that bodywork prep and have it be ruined when scratches start appearing 6- 12 months later. Joined: Mar 24, Posts: Profile Page. Take all your body filler to grit that will stop the shrinkage from showing up later and dont shortcut, go 80, then then and finally Then prime it.
Joined: Jan 29, Posts: 87 Profile Page. Matt Kvamme , Mar 31, Joined: Sep 17, Posts: Profile Page. If you go too coarse you loose a bit of adhesion and risk scratches coming back. A heavy bodied product needs something to hold on too. So I have a question. I'm blocking out a door.
I had one area I didnt' sand the iniitial scratches good enough I'm thinking they were still 80 grit. The 1st time I primed and blocked it the scratches showed up. Now after the 2nd and 3rd time of blocking they are gone for now.
Will they show back up? I'm concerned I need to take this back down to original paint and sand them out then rebuild with primer. Lately I've been dry sanding all my blocking with if I have to recoat with more primer.
Then before paint I'll block everything with wet. I normally have always wet sanded with before paint and can't say I've ever notice grit scratches showing up. The project I'm doing now is a complete repaint so I have all the panels in primer. So I'm not painting directly over any original finishes. I pretty much disagree with this whole thread. First of all we're not talking about lacquer primer that will shrink and expand indefinitely.
You should be able to spray primer over 80 grit with no problems with shrinkage later as long as the primer has had enough time to chemically harden we're not talking days here to harden either. You should be able to prime over 24 grit and not worry about shrinkage as long as you let the primer dry based on that primer companies recommended drying times. You can make it as simple or as complicated as you want. Most of the time people over complicate it.
What you're failing to realize is that body filler, poly primer, 2K primer and paint are different materials and can expand and contract differently when the surface changes temperature. It lets the primer do any shrinking and become stable. Start with a heavy-grit sand paper, such as grit. The heavier grit will cut the surface level rather than follow the contour of the high and low spots.
Re-prime with primer surfacer and sand with or grit to smooth it out. Most, if not all, of the primer surfacer will get sanded off as the body is block sanded. Although primer surfacer is often referred to as high build primer, it should not be used as body filler. That leads to shrinking and waves. Do good bodywork. A guide coat will show you if the panel is as flat and smooth as possible.
What you want is a contrasting color. You don't need to cover the primer, just a mist coat is all that's needed. If you remove all the mist coat fairly evenly as you're sanding, that's good. If you are leaving areas that aren't sanded, those areas are low. If you remove some areas all of a sudden, those areas are high.
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