Auto Paint Repair

Self Etching Primer vs. Epoxy Primers


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Self etching primer and epoxy primer have different uses when you’re preparing a vehicle for painting. Both can be important to the process, but each has a different role. It’s important to know what self etching primer can do to help you and when to use epoxy primer. Being knowledgeable will help the final painting of your vehicle as well as the finish and it's durability.

Self Etching Primer

After you remove the rust scales from the metal on your car, you need to apply self etching primer. It’s a mix of phosphoric acid and zinc. The way it works is that the acid forces the zinc into the top of the metal. It’s purely a surface coating, and it doesn’t stop the rust. It does, however, prevent the rust problem from worsening.

You need to make sure that you apply self etching primer to bare metal that’s been thoroughly cleaned in order for it to be fully effective. That means cleaning off everything, even fingerprints, which can leave a little grease.

Using Self Etching Primer

You’ll notice that the self etching primer is usually a grey color. This simply lets you see where you’ve applied it. You should only use a single coat of it as it is meant as a cover for rust more than anything else. Unlike other primers, you can’t use self etching primer then keep the car outside until you’re ready to paint it. You need something else to seal it such as filler (and more primer) or high build primer, which serves a similar function to filler. You can buy self etching primer as a spray or in two parts to mix together and apply to the car.

Epoxy Primer

Epoxy primer is excellent for work on cracks and dents. Much like a high build primer, you put on layers of it to fill the dents. It bonds very well and makes a good surface to which paint adheres well. You can us it on top of self etching primer to build up to a level surface.

You need to have a dry, very clean surface before you can apply epoxy primer. It comes in two parts which need to be combined and mixed before they can be applied. It’s important that you mix them thoroughly, taking several minutes. If you don’t, the epoxy won’t bond properly.

Applying Epoxy Primer

Start by just applying a thin coat to the area you want to cover and then leave it. It doesn’t have to be completely dry before you put on the next coat, merely sticky to the touch.

Keep doing this, building up thin layer over thin layer until you’ve reach the thickness you need to fill the dent or crack. At this point, you’ll leave it to dry completely. Only after that can you sand it down. Once sanded and cleaned of all the dust, you’ll be ready to paint the vehicle. Self etching primer and epoxy primer work together, rather than against each other. They both help you prepare the car for painting.

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