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Epoxy primer is lifting.
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Chris333
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PostPosted: Tue Jul 10, 2018 2:59 pm    Post subject: Epoxy primer is lifting. Reply with quote

I sand blasted 90% of the whole front end of my car and sanded the rest of it down with 36 grit. All 4 fenders as well. After test fitting the fenders a few times rust started to form. I sanded most of that down. Everything was finished with 36 grit.

Before spraying I washed it all with Prep & Etch:
https://www.homedepot.com/p/Klean-Strip-1-gal-Phosphoric-Prep-and-Etch-GKPA30220/100406369

On my first fender I washed it off with the hose, but before I could get 20 feet to the air gun it was rusting. So I re-washed it with etch.

This time I washed everything off with Prep All.

Sprayed the 4 fenders and front clip of the car.

Today I started spreading filler and as I sanded it I saw small bubbles. I poked them with a razor blade and it was down to bare metal. Kept going and more bubbles. Ended up pulling about 2 sq ft of primer up with the razor blade.

What the heck should I do now? and what went wrong?

How do I test the fenders to see if they need re-done?
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jspbtown
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PostPosted: Tue Jul 10, 2018 6:34 pm    Post subject: Re: Epoxy primer is lifting. Reply with quote

My guesses?
1. Residual contamination prep & etch
2. Incorrect mixing of the epoxy and hardener.

#1 is my first guess
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Chris333
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PostPosted: Tue Jul 10, 2018 7:02 pm    Post subject: Re: Epoxy primer is lifting. Reply with quote

Is there any sort of test I can do or does it all need stripped again?

I even put fresh undercoating inside the fenders Crying or Very sad
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Q-Dog
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PostPosted: Wed Jul 11, 2018 5:53 am    Post subject: Re: Epoxy primer is lifting. Reply with quote

Strip it all.
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jspbtown
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PostPosted: Wed Jul 11, 2018 6:29 am    Post subject: Re: Epoxy primer is lifting. Reply with quote

I agree with QDog. While frustrating to have to strip just the epoxy off you can probably imagine how much more frustrated you will be when your expensive paint starts peeling off in sheets
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theKbStockpiler
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PostPosted: Wed Jul 11, 2018 8:26 am    Post subject: Re: Epoxy primer is lifting. Reply with quote

Phosphoric acid removes rust or converts it. As far as prepping goes ,that refers to concrete.If the acid is left to dry on bare metal or paint it leaves a residue so I would be sure to remove that before putting anything on top. I think 100% phosphoric acid causes some flash rust and does not actually prevent it. If you mix it with water like the directions say to 'phosphatize it' ,it does not cause flash rust but still leaves a residue.
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Chris333
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PostPosted: Wed Jul 11, 2018 8:54 am    Post subject: Re: Epoxy primer is lifting. Reply with quote

I tried to leave the acid on wet for 30 min, but it was probably less than that. One of the Eastwood videos said to leave it on for 30 min. and then they washed it off with Prep solvent. I gave it 3-4 coats of prep-all:
http://www.kleanstrip.com/product/prep-all


Took me a month to get all that metal stripped down...
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theKbStockpiler
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PostPosted: Wed Jul 11, 2018 9:33 am    Post subject: Re: Epoxy primer is lifting. Reply with quote

The PrepAll is a solvent like Acetone or any other cleaner that breaks a substance up but does not move it anywhere. That's why in the directions they say to wipe it off with a rag. The PrepAll will evaporate and leave whatever was on the metal still there. Or maybe your hardener is bad. You counld do a test on clean metal or even cardboard and see if it still happens. Confused
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Chris333
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PostPosted: Wed Jul 11, 2018 3:29 pm    Post subject: Re: Epoxy primer is lifting. Reply with quote

Today I sanded down the whole front clip from door to door. I found a few spots that didn't stick.

I think the problem was that I sprayed the acid on and wiped the cleaner with a rag. So the spray got into all the small spots and the wipe didn't.

At least this time in bare metal I won't need to do the acid.


Also with the metal being down to 36 grit it had tooth, but after the acid it seemed to be smooth somehow.
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Chris333
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PostPosted: Wed Jul 11, 2018 7:17 pm    Post subject: Re: Epoxy primer is lifting. Reply with quote

What do you guys suggest for the wipe down before spraying?

Is the preps all good enough?
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Teeroy Premium Member
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PostPosted: Wed Jul 11, 2018 10:57 pm    Post subject: Re: Epoxy primer is lifting. Reply with quote

Check the data sheets on the epoxy you are using. Some are not compatible with etch or etch primers and will lift or peel.
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jspbtown
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PostPosted: Thu Jul 12, 2018 6:41 am    Post subject: Re: Epoxy primer is lifting. Reply with quote

Let me first start off by saying I am NOT a professional. But I have painted several cars and panels.

That being said....I always like using straight alcohol as my final wipe down before paint. I use the preps all to get rid of the grease and/or silicone and then use the alcohol right before the paint. I seem to get better results this way. Might just be me...who knows.

I assume you are also wearing latex gloves?
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Onceler
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PostPosted: Thu Jul 12, 2018 6:55 am    Post subject: Re: Epoxy primer is lifting. Reply with quote

Im not a pro either, but i have used ospho (a similar acid) under epoxy, however I always let it dry overnight, then wipe down with wax and grease remover (i just use vm&p naptha from the hardware store).
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