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Old 04-16-2021, 07:09 PM   #9
CC69Rat
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Join Date: Jan 2011
Location: Chattanooga TN
Posts: 6,205
Re: Sanding grits on bare metal before primer and after

Just to add to what has already been suggested ..

Sand / Media Blast to bare metal. See what youre working with. Rust, patch panels, dents, etc. Once you have the metal as straight as you can with a hammer / dolly, start with your Direct to Metal Filler. I like the UPOL products, anything by Evercoat has been great for me too. It just depends on what you have to repair. I try to fill and sand as much as I can at this stage for a few reasons, I'll usually sand with 80 to get it flat and 120 to reduce sand scratches or recoat if necessary.

Once it's semi - flat or to the workable stage I will spray it with Epoxy primer. As the other guys have mentioned, you want epoxy on the bare metal. I like SPI too. Good stuff. The key here is youre trying to "seal" back that bare metal and body work. You want that underneath your primer coats as a barrier for your your bare metal. There's a difference between Epoxy primer and your regular 2K build primers. Epoxy will protect the metal from the elements. 2K primer is porus.. water can get to the bare metal if the epoxy primer is not there. So, you do all this work and spend all this money just to have water get to it and rust will form underneath your primer. It's a mess. It may take years for it to happen, but it will happen.

The biggest thing (for me) is I try to finish up all my body work before Epoxy. Here's why. Epoxy dries up really hard. It makes that seal underneath your paint. It has a working time window. Once you spray your epoxy, you have 7 -10 days MAX before you'll want to spray your 2K primers and start blocking. The 2K primer has to form a chemical bond to your Epoxy primer. If you let the Epoxy sit on the panel too long, it gets so hard, it's not only difficult to sand back off, but it just will not bond to your primer coats as well if you exceed that 10 day mark. If you spray Epoxy now, then try to body work the panel.. chances are it will take longer than 10 days. It does for me anyway. If you do let it sit for longer than 10 days, I'd suggest knocking it back off and re-spraying it.

So, bare metal - 80 scratches. body work, Direct to Metal filler / Hammer work. Get it flat. Filler skim coat, 80 /120 on a flat block. Epoxy Primer. 7 - 10 day window, I usually hit the epoxy with a red scotch brite pad then tack it off and spray my first pass of 2K primers. Block, sand, repeat, Final skim .. etc. If you blow through your primer as youre blocking it, and get back to bare metal.. hit those spots with more epoxy primer as needed. two light coats of 2K build primer and reblock it. 120 / 220, two more light coats. 320 / 400. If youre going with metallic top coat I sand to 600 minimum or you'll see sand scratches in the finished paint (the metallic will settle into the fine scratches) 500 for non metallic or Single Stage. Sealer , base, clear, .. and youre done.

Hope this helps. Good luck with it man. Im no pro, but I'll help you any way i can.
Later.
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Last edited by CC69Rat; 04-16-2021 at 07:14 PM.
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