So I'm almost ready to shoot my 69 Charger it's original B5 blue. All of the body work is done. The whole car has been primed with a high build 2k primer, guided, and blocked with 220 on a long board. My question is, since the B5 is such a bright heavy metallic, I've been reading on the web to wetsand the primer with 400-600 before shooting the base. This seems a little too fine. I did one side of the car with 500 already and it is very smooth, almost too smooth. I'm worried about adhesion. I want to make sure the paint has something good to bite onto, but I also want to make sure the metallic flows nice and smooth. Does anybody have any experience/advice when it comes to finish sanding primer when using a metallic base?

600 wet is plenty enough for mechanical adhesion. It will feel smooth but the basecoat will adhere. If you shoot it over 220, you will see every sand scratch in the primer. Personally I would finish the primer with 400 wet, then use a reduced coat of epoxy primer as a sealer before basecoat. Plus the benefit of epoxy is that it will tie the coats together chemically, as well as a uniform colored ground coat.

what does the tech sheet recommend for final sanding?

when I daily spray PPG DBC base coat I final sand with 400 dry, 600 P grade wet is about the same, apply sealer then clear.

when wet sanding what is the grit rated? there will be a P behind the numbers for P grade. P grade is usually black and is the most readily available now. A grade is usually gray with no letters behind the numbers. P grade has coarser grit and you should use 1 grit higher than A grade paper.

Not sure if your car is assembled, but I shoot all my cars dissasembled, with parts hanging especially on high metallic cars. You get a much more even flow and less chance of any light or dark areas. Once base coat is dry, I wet sand with wax and grease remover before clear coating using 600-800 grit paper. Alot of people will say not to use Wax and Grease remover but for me it works alot better than water because it flashes faster and you know it is clean and not contaminated with the garbage that your water may have in it. Be sure not to sand past your current coat of base. if you sand a metallic beyond the first coat, you will have discoloration and you will have to re-apply another base coat. Then put plenty of clear over it and if you have any issues with the clear, you can wet-sand the crap out of it as long as you dont break through it. If you break through the clear coat then you are in trouble. Here is an example of the process I do on my cars. This car was sold at Barrett Jackson a few years ago for 40 grand Barret Jackson . I painted it in my garage using this process. It was a one of one known to exist numbers matching Auto. 383 Notchback. This was a very heavy mettalic car, but as you see it is straight as an arrow and paint is immaculate. But to answer your question, 600 is good, anything less could end up with scratch marks showing up after clear.

Very nice looking car at Barrett. Great color combo.

I wetsand primer with 400, good 3m or similar paper. If it's painted areas, I used 600. If you don't use something than finer than 220, your going to see it especially with a metallic color.

When wetsanded with 400, you can actually see a little shine in good light and look it over for flaws too.

400 is typically OK for most paint, 600 is better for a smoother finish.
As the other poster said, when your substrate is looking shiny, the top coat has the best base to build to a shine instead of a rough surface to try to blend in.
The topcoat paints do not really fill in the sand scratches and they will be visible in the finished paint.

Paint fills in/hides nothing. I've had good luck with painting over 400. What do the P sheets for the paint you want to use call for?

Oh, By the way, Don't ever use any of that red filler in the tube like you get at the parts stores. It will shrink big time and eventually cause issues. Make sure whatever you are using is good quality fillers. On the Cuda I restored I used Evercoat Rage Extreme and I think USC Half Time for finishing filler. That was a few years back, so there is probably something better today.

I switched to rage ultra myself in the past year... not cheap at 55 a gallon, but it sands easier than polyester finishing putty. Really with it, you don't even need a finishing putty.

Yup definitely a lot easier sanding, but spendy. Sands down very nice and smooth.

For the time saved in sanding, sand paper and not needing much finishing putty... it more than makes up for the cost. I wish I would have learned this years ago. I hated the idea of spending 50 for a gallon when I could get decent stuff for 15.

For sanding with 600 grit before the paint, what exactly are you guys using?

Do you use a foam block, in an X pattern like when sanding a guide coat?

I agree completely. B5 has a fine metallic and the flake will lay down in every sand scratch you leave behind. Final block with 600 minimum. On final wash and prep we use 1000 on a soft pad with soap to go over the entire car and hit any scratches.

Yep, I took a class at the local community college and he said high end paint usually will get blocked in 600, then 1000 on a soft pad