How to scuff up epoxy primer in order to spray the top coat?

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Bill Crowell

Bill Crowell

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I painted the underside of one of my Mopars with Nason Ful-Poxy 491-12 epoxy primer and then, dangit, life intervened and I didn't top coat it in a timely fashion (48 hours)! To make matters worse, the surface of the underside of the body is very irregular, with many flutes and louvers pressed into the body panels, so it will be relatively difficult to sand. The technical data sheet for Ful-Poxy says to sand it with 400 grit and then 600 grit before top coating it at this stage of cure. I have some questions for you body men: how about using Scotchbrite pads instead? Wouldn't that be easier than using sandpaper? What grade of Scotchbrite? Any suggestions about how to sand a highly-irregular surface like this the easiest way? Thanks very much.
 
im in the exact same boat as you.. i will be watching for suggestions also...Rich
 
My guess is red scotch brite. Then wipe with wax/grease remover. TopCoat.
Disclaimer: I am not a pro. Thats why no one figures my body work worth $9000-10,000 per job.
 
Scotchbrite will just scuff the surface, it will not remove imperfections.
Sorry, wet sand with 400 grit paper, do it right.
 
red scotchbrite. If your worried about imperfections and making it perfect you will have to follow up with a surfacer primer. Nason, as with most epoxys really are not sandable. Sure they will sand but not easily and the finish wont be great.
 
If your goal is to have the bottom look as good as the top, you need to apply high build primer and sand it smooth. since 'life got in the way', you do need to scuff the epoxy primer for mechanical adhesion. I have been sanding epoxy primers for many years without any problems.
If perfection is your goal, I would lightly dry sand the epoxy with 320. I am talking about the kind of sandpaper specifically made to block sand primer with. Then apply your favorite primer and sand it until it is ready for paint. I would use Evercoat G2 polyester 2K primer and sand with 320 dry followed by 320 wet and 400 wet. I'd go to 600 wet if I were painting metallic.
If you just want it to look good, I would lightly sand the epoxy with 320 dry followed by 320 wet and 400 wet (then 600 wet for metallics). Then, with proper mechanical adhesion, you can spray your paint.
PERSONALLY, I would go the primer route. It isn't that much harder, it will look better and you will not regret it.
 
If you want it real nice sand the epoxy primer with 180 or 220 spray 3-4 coats of 2k high build primer then sand with 320-400 then spray your top coat or if your not being that picky scuff it with a red scotch bright pad then spray your top coat
 
Red Scotch Brite, then blow it off, tack off the large flat areas, then put your nice finish on there.

Just want to break the surface to give it a little tooth for adhesion.
 
Not sure ok n the brand you have but PPG says after the open time for chemical adhesion to ride so you can have mechanical adhesion. This is on the tech sheets. Thet say or used to n It th sand so we always used red 3-M pads. Then shot Evercoat sandable primer. My Favorite is Slick Sand.
I went overboard and shot it with 2 coats sanded, shot 2 more coats and wet sanded with 400.
Shot R-M Diamont Base and clear.
Was not to bad as a friend and I passed the gun to each other as we shared the job. As it was quite a long job to shoot it on jack stands

BOTTOMCLEAR8.jpg


BOTTOMBASE1.jpg
 
Thanks for all the good information. Yes, barbee6043, it's the underside of the car and I'm going to top coat it with some PCC industrial semi-gloss black catalyzed urethane (single stage), so I'm not all that concerned about how it looks, so I think I'll just use the red Scotchbrite pads, call the scuffing good and then spray the urethane.
 
^^Scuff with the red and wipe it with oil/grease cleaner..... you can make the single stage plenty shiney with the slow reducer sprayed when the weather is right.
 
Bill Crowell said:
Thanks for all the good information. Yes, barbee6043, it's the underside of the car and I'm going to top coat it with some PCC industrial semi-gloss black catalyzed urethane (single stage), so I'm not all that concerned about how it looks, so I think I'll just use the red Scotchbrite pads, call the scuffing good and then spray the urethane.
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That makes sense to me. Jeepers, at first I thought the car was going to SEMA!
:rofl:
 
Bill Crowell said:
Thanks for all the good information. Yes, barbee6043, it's the underside of the car and I'm going to top coat it with some PCC industrial semi-gloss black catalyzed urethane (single stage), so I'm not all that concerned about how it looks, so I think I'll just use the red Scotchbrite pads, call the scuffing good and then spray the urethane.
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OK. Since you appear to be going for a nice semi-gloss black underside, the scuffing will work fine. That isn't how I do it, but I am old and set it my ways. Just be careful about one thing! You need to THOROUGHLY scuff it. If you leave any shiny spots, those spots will NOT have 'tooth' or mechanical adhesion for the paint to stick to, and you will have problems down the road. Also, please note that like sandpaper, a piece of scuffing pad does not last forever. when it stops scuffing/cutting, switch to a new piece. and make sure you wipe/clean the scuffed surface down with a pre-paint cleaner and hit the surface with a tack cloth. Good luck, and POST PICTURES OF YOUR RESULTS.
 
.I would also still recommend looking at the tech sheet before just scuff and shooting. You do not want stuff peeling off later.
The PPG sheer says after the open window has closed to scuff, and reshoot with a coat of PPG DP40, 90 etc
I would assume it is a mechanical and chemical bond. Then a top coat of primers or paint.
Most manufactures have tech sheets I would advise you to read it for the products you are using
 
I’d be half tempted to hit it with a light, fine media blast and more epoxy.
 
Scamp Rhonda said:
That's what I was thinking too but I'm not a pro so I was hoping someone else would chime in. Thanks
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It’s hard to say without physically being there. Sand the easy areas and lightly blast the hard to reach areas. The problem is media in all of those nooks and crannies.
 
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Reason they say scuff is most epoxy gums up paper.
It is intended to be coated over while open. If not then suffed and recoated with more epoxy.
I use also epoxy ( PPG) as,a,sealer ontop the final sanded high build primer before paint as a sealer.
Insurance
 
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Overthinking!>>??
The good thing about epoxy primer is its ability to stick to just about anything ( except silicon and oil_.
IF so darn concerned, scuff with the darn red Scotchbrite, shoot a coat of epoxy ,and at the CORRECT TIME FRAME< shoot the friggin topcpoat!!????????:poke:
 
Oops, so maybe I didn't read the technical data sheet for the Nason Ful-Poxy epoxy primer carefully enough, but I'm noticing where it says, under "Dry Times", that "Ful-Poxy can be recoated at any stage of cure". Doesn't this mean that, rather than scuffing up the old primer, I could instead shoot another coat of Ful-Poxy and then spray the top coat OK?
 
Bill Crowell said:
Oops, so maybe I didn't read the technical data sheet for the Nason Ful-Poxy epoxy primer carefully enough, but I'm noticing where it says, under "Dry Times", that "Ful-Poxy can be recoated at any stage of cure". Doesn't this mean that, rather than scuffing up the old primer, I could instead shoot another coat of Ful-Poxy and then spray the top coat OK?
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Yes after you scuff it "So you have adhesion"
 
Bill, i know the pain.... ive been sanding epoxy for days... my finger tips are raw from reaching into those little areas, im doing the trunk and interior now. I wont make that mistake again when i do the underside,,, epoxy one day and high build the next day followed by a light sand and then top coat....
 
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