Projects body filler over epoxy primer or bare metal?

I'm almost ready for body filler on my 35 Chevy. I've heard people talk about spraying epoxy primer first.
Can anyone tell me the benefit or not when using epoxy primer?
thanks..........

 

I use PPG DP90 over bare metal and then body filler. Epoxy should be sanded lightly after drying for 24 hours. Works for me. Problem with body filler over bare metal is trapping moisture and/or rust starting before you can get epoxy applied. If you sand back thru epoxy be sure to apply epoxy to bare surfaces.

 

I used a skim coat of Rage Gold over sanded bare metal on my '36 coupe 5 years ago and primered & painted over it. The car was unavoidably stored for a year in a metal, rented garage during a summer of 100* days and in my new shop during the following winter of below freezing temps. The paint looks nothing worse for the storage and looks as good as it did 5 years ago. I expect it will look as good 10 years from now.

 

Here we go.
Done it both ways.
No issues with either.
Just follow whatever products you use instructions

 

I'm of recent with epoxy over work, then 2K build primer..
That's with clean metal..
If I had something completely rusty, sanded/blasted, Ya I would epoxy first..
Make sense..

 

Straight from the 3M rep todays filler works best over Ecoat when done proper so going over Epoxy is fine. If you are doing a repair score the bear metal with 80 grit finish the repair prime seal and paint.

 

Beat to death topic, just use the search function and read the extremely numerous threads and posts.

And no, nothing new in products since the last time it was asked 2.months ago.

 

thanks for everyone's help!!!!!

 

I'm no expert, but I always seal with epoxy primer sealer first. Bare metal can flash rust, so if you stripped the body to bare metal any filler should be applied immediately or it will flash rust and that's not good to have under your filler.

 

Florida in the summer everything rusts within 30 minutes, very annoying.

 

I have to admit that this etch priming seems to have a lot of contradictions. I'm looking at doing some right now. Along the way I have read that the original DP90 was reccomended directly over bare metal and sandblasted bare metal. That you should not use clean and etch chemicals if sandblasted because it will stay in the deeper pitting. That you should not use clean and etch chemicals because they actually work against the adhesion of the primer. That the epoxy primer gets so hard that nothing wants to stick to it. That body puddy sticks better to it than it does to bare metal. That you should sand it, and that you shouldn't sand it.
I'm trying to do this right, but it just seems that everyone does things differently.

 

Epoxy primer, then filler.

I have been doing it that way since my first 3M rep said it was fine.

It has been fine since.

 

I've also done it both ways with no problems. I live in So Cal, and the weather here is fairly consistent. If I lived somewhere where it was hot/humid or rainy, I would epoxy prime first.

 

I started about 30-years ago, when I lived in Southern New England, with its Summer daily monsoon rains.

I carried it forward when I moved to California. Where I am it can still get humid, from the fog.

 

Nowadays, I’m in the camp of epoxy over clean bare metal first, then filler where needed. Living in the lower Midwest where it’s humid more days than not, you don’t want to leave bare metal unprimed for very long. I do recall though back in the early 80’s, sandblasting a burnt cab, body filler right over the bare profiled metal, filling primer right over that. Blocked and primed a couple more times and then painted. Held up well for many years. I think the key is try to not leave things open to draw moisture for any longer than you have to.

 

Either way, but I do the Epoxy, or I have had a complete car/part dipped in zinc coating then Powered coated black.

 

****s confusing. I teach it. I love the looks I get explaining this topic.
Etch isn’t used under epoxy as a wet on wet application.
Etch is generally used under urethane in the collision industry.
Epoxy is generally used in resto work.
Urethane products can go over both.
Polly primers generally go over epoxy.
Some Pollys can go over etch (read the tech sheet) but takes longer to cure.
Etch was basically designed to eliminate metal prep cleaners.
Most people don’t use metal prep products with epoxy. That was standard operating procedure when I started decades ago. Many epoxy tech sheets Ive read usually have a line “for best results use **** metal cleaner”
If you sandblast then DA, it’s no longer sandblasted. It’s sanded.
Clear as mud

newer higher quality fillers are designed to go over cured, properly sanded finishes

 

I am currently using my 85º+ shop to cure epoxy!

 

That’s a cool day here in Bama

 

You have to watch that paranoia stuff it will rule your life if you let it. Lippy

 

Paranoia will destroya!

 

Paranoia runs deep ,in to your lives it will creep .....

 

Thanks Anthony...........

One more question. What is the difference between a "catalyst" and an "activator" ?

Make that two questions. I have some unopened (and some opened) paint that I bought several years ago.
I have both epoxy primer and high build primer and an unopened gallon of black. (Kirker brand)
I was planning on using that to paint underneath the body and inside the body as I think the glossy surface will repel water and dirt and hide road mileage grime. Maybe paint the frame as well if I have plenty although I still have to build the frame .

I have looked for some shelf life info but haven't seen anything on the cans saying there is one or that the stuff goes bad after opening. I have the Enduro Prime and its "catalyst" and have urethane and its "activator".
Hate to throw it away......but if I hafta, I hafta. Value your opinions and experience. Waddayathink?

 

Activator, hardener, catalyst are all the same thing as long as you are using the right one for the product you are trying to harden. It is not a good idea to mix brands. As far as longevity they start to lose their strength as soon as they are opened and they are the component that fails when something goes wrong about 99.9% of the time. How old are they? Shelf life for most automotive products is 12-18 months. Do a test panel and see if they cure. For inside and under the car probably not a big deal if they cure. I wouldn't use them on the outside of body, to much work to risk having them fail down the road for what it costs to replace.

 

Got

By chemistry terms, a catalyst speeds up a reaction and a activator activates a catalyst. I’m not a paint chemist. Those guys would need to expound on the differences. But like stated above are needed in the correct ratio stated by the paint maker.
Shelf life? Also like above. Depends on if opened or not for activators, catalysts and hardeners.
Unopened shelf life? I’d contact the maker.
The old paint you have should be fine. Stir it up very well.
All the solids settle to the bottom.
If in doubt, spray a test panel and see how it does.
I’ve had some very old industrial epoxy do ok. But wasn’t for a car.
I guess ya have to weigh out the risk vs reward.

 

They are a lot older than that. I tried some on an old hood yesterday. It seemed to work fine. I have a paint shaker, so I shake everything well. Right now I'm just trying to get the underbody coated and inside coated with the older stuff. Not anything anyone can see, so if it isn't beautiful.....thats ok. Just want a rust preventative. The old "catalyst" that had been opened looked a little "unmixed" till I shook it, and the coat on the hood looks and feels pretty solid.That was using an opened leftover of the epoxy primer. (Kirker brand) I have a brand new can of Catalyst that is unopened (gallon). Thinking about getting a new gallon of the epoxy primer. That would give me enough to spray two vehicles underneath and inside. (Son's truck supposed to get blasted in a week or two). Then I have an unopened gallon of gloss black that I can put over the primer if I get new "activator".
Then I would get all new primer and paint for the external body surfaces.

 

Just be aware that the issue with age and any catalyst/activator is that they weaken with time, open or not. It's not an all or nothing situation. The longer they sit they weaker they get. What that means is that you are not fully curing whatever product you are spraying (even if they get hard) so they will not have the same integrity as a fully cured product. That means they can shrink over time, they can continue to move over time, they can be less UV resistant etc. How you want to use them, inside and underneath, probably not a big deal.

 

A very long read--but still relevant and answers all the questions. https://www.jalopyjournal.com/forum/threads/body-tech-bondo-101-magic-dent-erasing-compound.8318/

 

I pulled a little exerpt from each post because I wanted to show each of you how much I really appreciate you taking the time to share your knowledge and experience with me. I have learned a lot from what you have written, and I know that some of you put a lot of time and effort into your explanations. So, THANK YOU

 

Keep reading and keep asking questions, then practice on some s**** panels to improve your technique.