What steps of sandpaper blocking primer

Gmills

Promoted Users
I am in the middle of a restoration and have little experience. I have done one other job that turned out really well but was a large learning curve. I have some panels that I have blocked the first round of high build primer with 80 grit and they are really close, just a few minor low spots. After the second coat, do I use the 80 grit again to get it all even and then go to 150 then say 400? I guess I'm asking what sanding steps you guys go through to get it right and will I need a third coat? The last one I did I blocked the whole truck three times from start to finish with 400. It worked me to death and I'm sure it could have been better but it turned out really nice.
 
When I need one really straight I'll sand the primer with 150 or 180.
Then guide coat again and finish sand with 400 wet or 600 dry until the 150 scratches are gone..
I don't reprime in between unless I have sanded through the primer the first sanding.
I see no point in sanding primer more coarse than 150, that's pretty coarse.
 
I agree with Jcclark but vary just a little bit in my process.

The coarser grits, like 80, are used on a long block to get your panels straight and wave free. The key to block sanding is to change the sandpaper often and do not press so hard on the block you flex the panel.

If you are pretty confident the panels are straight then shoot your 2k primer coats. When cured you should apply a guide coat (I use 3M Powder) and then block sand with say 180 grit just to remove the guide coat. If you can do that without sanding to metal anywhere things are looking good.

At this point I (others may do it differently) shoot another coat of reduced 2k primer, apply guide coat again (yes a bit OCD) and then wet sand with 600 grit on a soft block just to remove the guide coat.

Clean, wipe with W&G remover (I prefer solvent based) and let flash off completely.

The I shoot a reduced coat (1:1:1) of epoxy primer as a sealer.
 
I'm no expert, but I'm in the middle of taking my car down to metal with razor blade and a heat gun. I suck at it but it works and keeps dust down in my garage.

My plan is to sand the metal with 80 grit on a DA, W&G with 700/710 then try to build with SPI epoxy and start blocking with 180 grit and see where I'm at. From there I'll apply filler where needed, sand with 80 and finish with 180 with glaze if needed. Hoping to do all the blocking with epoxy. I'll shoot another couple of coats of epoxy, guide coat and block 320, then more guide coat and hit it with 400 on a DA. Clean it with 710, seal it with light coat of epoxy (1:1:1), base then clear.
 
I would suggest 220 to get most of the guide coat off, then 320.

Yes sorry, meant to say I will block fully with 180. So after the initial epoxy coats and 180 to see where I'm at and use filler where needed--I will add 2 or 3 more coats of epoxy, guide coat, block with 180 to get it straight. 220 would be fine too. Then coat it again with epoxy for 320 then 400 DA.
 
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