Etch vs Epoxy primer

Epoxy-primer-header

This page discusses the differences between etch vs epoxy primer for use in cars or other restoration projects. New metal and other applications might call for a very different conversation. Some of the views in this post are from lengthy discussions with panel beaters and bodybuilders who work on cars daily.

Self-etching primers have been the go-to product to apply over bare metal on a car. The metal requires little preparation to apply, the primer dries and cures quickly, and it comes in 1K Aerosol cans for small jobs. DIY repairs and smash repair shops benefit significantly from these attributes. Quick, easy, and less time involved, which means cheap.

However, you’ve probably heard more people talk about epoxy primers and their use instead of self-etching primers. So etch vs epoxy primer? Lets start with etch primer.

Etch primer

The cost is cheaper, and the job is a bit easier. Stir the paint, thin it if needed, apply, and clean up. With fast drying and curing time, the job will likely be dry and ready for another coat if required.

Surface bond is achieved by acid etching into the surface of the bare metal. Good for smooth (paint-stripped) metal. If the surface being painted is too smooth then paint is more likely crack, peel or flake off. Therefore, all paints require a good physical bond on the substrate and subsequent layers to stick to. This can be done mechanically by sanding or sandblasting or chemically. An etching primer can be used on metal that has been stripped chemically, 

Applying body filler directly to etch primer is not recommended. Because the fresh filler can react with the acid in the etch primer, therefore, penetrate and loosen the self-etch.

It remains reversible forever so that subsequent coatings can soak in and loosen it. Wiping it with thinners on a rag will soften and lift the paint. Epoxy is not reversible; solvent or thinners will not affect it once it is cured.

Self-etch is not water resistant, so any place the paint might become chipped or damaged can provide a path to the metal and cause corrosion since etch primer is no protection against moisture.

Now on to epoxy primer.

Epoxy primer

More expensive to cover the same surface area as etch primer. However, when it comes to a restoration project, spending a few more dollars at this stage can save you thousands and better preserve the car.

It uses a mechanical bond and requires the metal to be media blasted or sanded before application.

Filler and etch primer are both porous, but epoxy is not, so epoxy provides a moisture barrier right at the metal where it is needed the most. Epoxy primer is waterproof and, in fact, can be used in immersed applications once cured. Epoxy primers and paints are the only choice when painting boats.

They seal the bare metal and stop moisture or corrosion from creeping in. Epoxy primer also seals the oxygen from the metal, leaving no chance of rust or corrosion forming on the surface. The sealing properties of epoxy mean that lengthy restoration work on an old car won’t allow rust to creep in before top coats are applied.

Filler can be applied directly over epoxy primer, and more epoxy can be applied over the filler to encase it in epoxy completely. Epoxy is specifically designed to be applied under filler, not so much for adhesion (filler sticks well to metal) but for corrosion protection.

Epoxy primers have excellent adhesion properties and stick to bare metal, paints, primers and fillers. This means you can hit an area with an epoxy primer sanded down to the bare metal, repaired with body filler, and then feathered into the original paint. Since epoxy primers adhere mechanically, they will grab onto most anything with a good surface texture, like after sandblasting. Therefore, it works well for stacking if you need to correct an area that you didn’t get perfectly flat and need a little more filler.

A misconception about epoxy primer is that it is thick and goes on like a ‘high build’. Epoxy primer goes on relatively thin and can also be thinned as required. Other epoxy coatings come as ‘high build’ and filler-type coatings that can be sanded or blocked to smooth out surface imperfections.

Conclusion

So one paint is not better than the other; they have different applications. As always, read the tech sheets and get the manufacturer’s information on the best ways to use each product in relation to your project.

At MP BLAST, we are not contacted when someone is doing a smash repair. We are contacted to do a full car sandblast for restoration purposes. We remove layers of unwanted materials like paint filler, primers and rust from the project’s surface. Our surface preparation results in a light shark skin-type feel, perfect for epoxy primers’ physical bonding characteristics.

When it comes down to etch vs epoxy primer, the clients we work with for restoration work prefer epoxy primer over etch primer.

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