The Stovebolt Site Forums The Shop Area Paint and Body Shop Epoxy Primer or Self-Etch Primer?

I am finishing up on the metal work stage of my '51-3100 restomod and will soon be looking at body work and painting. My plan is to media blast the sheet metal and primer it prior to body working to protect the steel. I have researched both epoxy primers and self-etch primers, both having their advantages and disadvantages, sandability, and compatability with bondo and hi-build primers. Any recommendations/procedures for either method for a beginner body worker would be appreciated. Any recommended publications on this subject would also be appreciated.

Thanks!

Epoxy primer for media blasted sheet metal is a no-brainer. It is a wonderful product.

There's no down side to epoxy primer. Self etching primer is a fancy way of saying sticky primer... and what good is a primer if it doesn't stick!?
Epoxy primer has the sole purpose of preventing rust; rust creep if scratched off and encapsulating any rust spores when applying it. If you want to risk rusting creeping under a scratch, then don't use epoxy primer.
Epoxy primer is very hard so it needs to be scuffed where you plan to paint it, just before you paint it. There's no substitute for epoxy primer, regardless of brand, they are all the same.

Nicely stated, Carl & Darcy

Self etch is old school, epoxy is the latest and greatest.
With that said, I have used self etch to put a real thin coat on top of bare metal to keep it from getting surface rust between weekends of working on it.

Thank you all for your input!! Sounds like epoxy primer it is. Thanks again!

Back in the late 70's to early 80's the auto manufacturer's were experimenting with galv type coatings to help combat the rust issues seen. On a PH level, these type coatings are slightly alkaline (base) and the normal primers used were ever so slightly acidic to promote adhesion. Combine the two together, and the base helps to neutralize the acid in the primer for less adhesion. (this same scenario causes adhesion issues when using Soda Blasting without properly neutralizing) Ever see pickups with paint peeled off in sheets? So their answer was to add more acid into the primer, hence the etch primer. The collision industry saw it used for many years afterward to insure the paint repairs would adhere to the factory metal. Today's autos are using more of an e-coat dip to seal and rust protect the body, so the etch primer is less used today. That, and they are finding that too much acid, if trapped under the paint surface, will cause a reaction, especially when exposed to heat (think car shows and hot sun) and will cause adhesion failure as the acidic process trapped under the paint releases the outer paint layer.

For rust preventative measures, and given a properly prepared and abraded panel, NO primer can match the properties of Epoxy Primer for preventing rust creep under the paint, to include many of the snake oil POR type products. That's not to say epoxy can't have issues though.... As mentioned, any residue from soda blasting (base) will have epoxy primer (slightly acidic) or most any other substrate falling off in sheets. IMO stay away from soda blasting to eliminate this issue, and use Epoxy Primer for the best rust preventative measure going today. Epoxies aren't used by the car manuf. as they take too long to dry as compared to E-coat. The factory processes are less about what is the best way possible and more about what gets this vehicle to the end of the line quicker.

Some paints are not compatible with self-etching primer. I used automotive enamel paint on some of my body parts. I was painting one piece at a time. I might as well confess. I was using Rustoleum automotive paint.in a rattle can. I was very careful with prep and application. It wasn't until after I painted some of my body pieces that I saw the warning "Do not use self-etching primer". The fenders looked perfect at first. After the paint had time to dry and cure the paint began to crinkle in several locations. The pieces with the standard primer (not epoxy) turned out perfect and still are.

Robert,

Thanks for the information. I definitely will NOT be using an etch primer. I am also staying away from soda blasting as I have quite a bit of surface rust as well as old coatings to remove and have heard soda blasting will not remove rust. I have been considering "Dustless Blasting" of my sheet metal components to avoid the possibility of panel warpage from sand/media blasting, followed up with epoxy primer. Your thoughts?

Thanks again!

Why are you blasting? The reason I ask is that coatings that are "tightly adhered" there's no need to remove them. If you have an abundance of rusty bits, blasting can help but only to a degree.

Old coatings do not need to be removed. New coatings will stick just fine.

Blasting saves time and energy but is not required in most cases, so if you have time to sand the panels, then epoxy coat them afterwards and you are good as gold.

I went to the Goodguys show in FTW last month specifically so I could spend some time with the PPG paint reps since I am getting close to that point on my truck. They really aren't recommending etching primer any more. Epoxy primer is a "direct to metal" primer. For the best quality paint job, the vehicle should be stripped to bare metal and immediately primed with epoxy primer, then body work can be done over the top of the epoxy. After that you use the high build primer which is also "direct to metal". No need to cover what was sanded with more epoxy.

Darcy,

Thanks for your input. I'm retired so I have plenty of time, but I'm blasting because I don't think I could achieve the same result with sanding as I could with blasting, especially in the hard to get to areas and crevices.

66rollback,

Very useful information, thanks!