Epoxy Primers when used on metal are for corrosion protection and helping with adhesion. It is a NON-SANDING Primer! The Correct Name Should be "EPOXY SEALER", because that's all it is! This product is a sealer to use on different surfaces for protection from foreign elements to eliminate contamination! But it's not the only primer that you can use for bare metal, it's just one option.
Etch primers are convenient for the priming of all types of metal that require a very quick turn-around time. They only require a very thin coat in order to etch the metal surface and create a tenacious bond. Zinc phosphate pigment offers some degree of corrosion protection. The fast dry characteristics allow the topcoat to be applied shortly after primer application.
Both Epoxy Primer and Self-Etch primer (Self-Etching primer) can be used on bare metal. Both provide corrosion protection, and both can be top-coated with primer surfacer.
If you’re doing some body work and you have some bare metal, you don't want to just put regular primer surfacer because it does not have the corrosion properties like Epoxy or Self-Etch.
So, how do you choose if you use Self-Etch or Epoxy?
It’s really just a preference and depends on a your individual variables. With a restoration shop, they're probably using more epoxy. If they're a high production shop, like a body shop that runs a lot of cars through, they're probably using Self-Etch.
The reasoning behind that, Epoxy is the only primer that you can put body filler on top of. You shouldn't apply body filler on top of a Self-Etch primer or primer surfacer, but with epoxy you can. Our opinion is if you're going to be doing some body work, the best thing is to put Epoxy Primer on top. That way, you seal it all off and prevent it from any rusting, and then you can do your body work.
Some advantages of Epoxy over Self-Etch:
Epoxy is very friendly (user friendly) and is very compatible with other products. You don't have to worry about anything lifting like you might with a Self-Etch primer. With epoxy, you can lay it over just about anything, body work, sanded paint, metal and you're going to be fine. With Self-Etch, if put it over different layers of paint, if put on too wet, it's going to lift because Self-Etching primer has acid in it. Be aware of this. Epoxy can be more expensive, but then again….when you are already spending hard earned money on restoring the car of your dreams, a few extra bucks isn't going to break the bank.
Some advantages of Self-Etching over an Epoxy:
It's a little bit straighter forward. There are no induction times with Self-Etching primer. There are 1K products that work well for corrosion protection, that are also available in spray cans. So, if you have just a small area and you're wanting to apply such corrosion protection to, a Self-Etching primer in a spray can may be the way to go. Very simple.
There are a lot of ways to do this. If you have a bigger area, let's say bigger than a gold dollar coin, you can mix up some epoxy and use that. If it's smaller than that, you could use a spray can of Self-Etch primer.
The advantages Self Etch over other metal primers are as follows:
- Provides excellent adhesion over a variety of different metals.
- Can be applied with minimal preparation (clean, degrease and abrade, refer to data sheets).
- Rapid cure, allowing over coating with thin film topcoats in substantially less than 1 hour.
- Zinc phosphate pigmentation offers some degree of inhibitive corrosion protection.
Lastly, there is one third option, and that's a DTM, Direct-to-Metal primer. This is a primer surfacer, so you get your standability with it. But it also has some acid in it, which acts like a Self-Etching primer. DTM can be applied directly to steel and then sanded just like a primer surface.
Important Notes: On epoxies, some have an induction time. Think of it as they have to kind of get to know each other a little bit before they bond.