How much paint to remove
 

Getting the 912-6 ready for paint. Changing colors from brown to orange. This is purely a track car. There are 2 coats of brown on the roof, front fenders, and doors. How far should I take these down in paint prep? Should I sand down to factory primer, or take the second coat off? Or should I just run off the large areas with 320 and do the detail areas (like the rain gutter) down to bare metal?

Thanks,

Other than the color not being what is wanted, does it have any paint issues? Peeling, blisters, cracks, etc? If it is good paint, I don't think that I would try to strip it, nor would I think it were really needed.

Do you mean doing it by hand?.

If all panels are smooth and straight, you can wet sand each, with a wet sanding block and fine 400 grit sand paper. Use sealer primer and paint/clear.

If fixing slight imperfections in any panel, you can sand by doing even sanding ("blocking"), using hand motions horizontal to 45 degrees, back and forth, dry sanding using a sanding block, small or large, rubber, wood, foam and/or a paint stick (with the paper trifolded the long way) works (using 80 grit). Don't have to go down to bare metal unless it has been painted various times or the paint is swelling from below for some unknown reason that sanding to bare metal would correct.

If the imperfections is/are really small fix it/them by wet sanding (again making sure to use the even motions described above) (using 180 to 220 grit), prime, wet sand with 220, prime, wet sand with 400, use sealer primer and paint. Should come out perfect with a little patience. Dont sand away all your primer undercoat and reprime and sand it all away again. It will get to the point when it is just right.

Also use wet sanding method to block out (remove by even sanding) any panel or area that you have previously blocked using rough or medium sand paper. Any area with small amounts of filler, and/or glazing putty, that you have previously sanded and primed, can be wet sanded with 220 or you could go straight to 400 wet. Followed by a few coats of primer over that area.

You are done when you have smooth straight panels that you sanded with 400 wet with no scratches of imperfections visible while looking at wet car in a strong light (can also wipe your areas you are wet sanding using a yellow scqueegie so you can see just when you have wet sanded just enough off, and the area is smooth. No scratches or imperfections are visible or able to be felt with your hand when you rub your hand over the panel. All areas that have some spots with primer should be smooth and have no scratches or uneven looking layers of paint/primer/filler/etc, showing It should just be smooth 400 grit sanded panels. Ok to have primer in small spots (don't have to always end up priming the whole panels). So long as have not sanded through to under layer. If you do sand through to any under layer but it is already smooth to 400 grit you can add just a light coat of primer and a light sanding so that you haven't sanded through.

When really done, spray entire car with sealer primer, paint/clear.

:) Notice I did not say to use a DA sander. Getting your work smooth and straight after DA'ing often still requires doing more by hand. Well at least it does in my book because I dont like the circular motion scratches of a DA that can swell even after you are done with the body work.

Good luck.

Regards,

My biggest concern is if it is an issue going over 2 paint jobs (factory and one other). I'm concerned about thickness and durability over the second coat.

Before you get started, how does it look?

In short, in the best case scenario, start sanding with 400 grit. Least is best, but that may be too idealistic.

If the area's finish is bad, eg. the valence, bumper is pitted really bad, you can sand it with 80 grit and go down as far as you have to remove the chip. scratch etc. If any panel is really bad you can block the entire panel with 80 grit and go as deep as needed.

When priming, your first coat should be light so you can make sure your present primer will not lift your previous finish (previous primer/ paint). Once the new primer covers and does not blister the previous finishes, you can proceed with second coat of primer. If it does and you have to resand you have to be careful with your first coat of primer from now on. Sometimes this happens and you can proceed with little correction. Sometimes it doesnt happen at all. I like to finish the body work and let it sit for a couple of weeks up to 4 weeks before final wet sanding and paint to be sure the prep is flawless.