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Old 04-05-2021, 10:21 AM   #1
88Stanger
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Sanding grits on bare metal before primer and after

Ok, so I am by no means anything close to a body guy but I have a very basic knowledge and like to lwarn, so with that said I have done all the rust repair and such and now I getting ready for 1st coat of primer/sealer. To start off I had the truck sand blasted so I am working with metal. I have repaired all the holes and rust areas and now I am getting it ready for the high bond primer/sealer.

1.) My question is what grit sandpaper to use on the bare metal areas before spraying the primer/sealer?

2.) After I get the primer on I will be using Dry Guide coat and looking for issues, use a cream filler as needed and then for final sanding what grit of paper do you use? I will be applying a single stage urethane Satin Red
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Old 04-05-2021, 10:45 AM   #2
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Re: Sanding grits on bare metal before primer and after

80 grit is usually recommended for bare metal before epoxy primer. I like 60 grit since it stays sharp a little longer.

For filler work you should start blocking it with 80 grit to level the filler, then apply guide coat and block with 180 until all of the 80 grit scratches are gone. Primer over 80 grit scratches will cause problems later when the primer shrinks.

Seal the bodywork with a couple coats of epoxy, then shoot a few coats of high build primer and block it again, start with 120 to get it straight. If you go through anywhere you can spot those areas in. Finish with 320, then 500 using guide coat in between.
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Old 04-05-2021, 10:50 AM   #3
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Re: Sanding grits on bare metal before primer and after

80 grit DA, metal should be free of rust, oils, and any other contaminants. Preclean with Wax and Grease remover, not lacquer thinner or other reducers. W&G remover is a slow to evaporate solvent that floats impurities to the surface where they can be wiped off before the solvent dries. Thinners flash off too quickly and can leave impurities that lead to fish eye. I would recommend SPI epoxy in black or similar for your sealing substrate. This sets up in a semi-gloss finish and turns a charcoal grey look when sanded, so essentially provides it's own guide coat, no need for the dry stuff.
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Old 04-05-2021, 11:15 AM   #4
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Re: Sanding grits on bare metal before primer and after

The perfect paint job:

http://www.spiuserforum.com/index.ph...-edition.2426/
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Old 04-06-2021, 09:45 AM   #5
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Re: Sanding grits on bare metal before primer and after

I honestly appreciate all the comments! God Bless each of you for taking the time out of your day to help me out. This is really good info.
Also, I looked at my primer and it is not an epoxy sealer, only a 2k primer. So now i am looking at getting some sealer. With that said, i have all new bed sides, doors, front fenders all new with the black protective coating. How do i handle them? Do they also need sealer?

Thanks again for your time
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Old 04-06-2021, 10:15 AM   #6
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Re: Sanding grits on bare metal before primer and after

The black coating the replacement parts come with is hit or miss. Sometimes it hides surface rust underneath or is easily softened by solvents, in which case it should be removed and recoat the panels with epoxy primer. Sometimes it holds up a bit better and people use it without issue. Given the costs of quality automotive paints these days, I'd rather be sure that the substrate and the prep under that is properly done and using quality materials.

Not all paints are the same, but I view 2K primers as your high build, and even though some claim direct to metal adhesion, it is likely not as good as the adhesion you'd get with epoxy primer.. Epoxy is what I spray first to seal off the metal from the elements and to provide a good substrate for anything that follows.
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Old 04-06-2021, 11:33 AM   #7
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Re: Sanding grits on bare metal before primer and after

88...I fell in that same trap...the IH is my 1st down to bare metal and back paint job..
I didnt know about spi at the time..and didnt know much about epoxy either..
But I mistakenly went to a auto parts store for my painting supplies..I knew from reading to use epoxy on bare metal..they gave me 2k high build instead..after I sprayed it on my bare metal, i started seeing rust pop thru it in about 3 weeks..had to resandblast all my parts and start over...this time I went to sherwin Williams auto paint store, and have been well pleased..
Wish I had known about spi at the time, I would have used their stuff..
I'm like Robert, remove the black coating, then you know what you got..
I heard it said if you wipe the black with laquare thinner and it doesnt come off, then its good..if it comes off ,then it needs removed...but I'd rather start with bare metal..
If Robert and John said to smear mayonnaise on it before paint, then I'd probably do it...hahaha
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Old 04-06-2021, 02:06 PM   #8
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Re: Sanding grits on bare metal before primer and after

Quote:
Originally Posted by mongocanfly View Post
88...I fell in that same trap...the IH is my 1st down to bare metal and back paint job..
I didnt know about spi at the time..and didnt know much about epoxy either..
But I mistakenly went to a auto parts store for my painting supplies..I knew from reading to use epoxy on bare metal..they gave me 2k high build instead..after I sprayed it on my bare metal, i started seeing rust pop thru it in about 3 weeks..had to resandblast all my parts and start over...this time I went to sherwin Williams auto paint store, and have been well pleased..
Wish I had known about spi at the time, I would have used their stuff..
I'm like Robert, remove the black coating, then you know what you got..
I heard it said if you wipe the black with laquare thinner and it doesnt come off, then its good..if it comes off ,then it needs removed...but I'd rather start with bare metal..
If Robert and John said to smear mayonnaise on it before paint, then I'd probably do it...hahaha
Thanks for input. I am going to pick up Epoxy Primer this afternoon or tomorrow just because of this. Thanks again everyone!!! I really appreciate your input and time to do it.
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Old 04-16-2021, 07:09 PM   #9
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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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Old 04-24-2021, 10:43 AM   #10
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Re: Sanding grits on bare metal before primer and after

Quote:
Originally Posted by CC69Rat View Post
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.
Thank you so much for the info. I have been working on final alignment of doors, figure it is best to do this before epoxy goes on.
May i just say, what a huge pain in the arse this is!! I am frustrated but i know it is just a matter of time.
It appears that the aftermarket doors i have do not nec. have level and flat door edges, so i may need to do some grinding of them them to be flat. lol I am going back out this morning to work on getting the doors fitment good before i spray on the epoxy.
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