EPOXY vs Etch Primer

M

moparmusclecars

Barry, please explain in some detail the advantages of using epoxy over etch primers. For some unknown reason many seem to believe epoxy is old school, and no longer used, and they seem to think etch is the way to go on everything that is bare metal. I would love to see you post a write up on the two, and what makes epoxy so much better. I see this issue coming up all over the internet consistently, and many are suggesting to others that etch is the way to go. I want to share with others the advantages of the epoxy. I know the differences myself, but figured I'd love to hear it from you! Thanks!
 

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etch primers were brought on by the oem failures of the 70's/80's . plastic media blasting then etch to avoid tear down and sanding. if anything etch is old school.
 
That's why reading the Paint/Body section of most car forums is a complete waste of time. People that have no idea what they are taking about. Etch is old tech, Epoxy is modern tech. OEM's recommend epoxy for all repairs, no OEM's that I know of recommend etch primer. As for the differences it's been covered ad nauseam here. Just use the search function. Main advantages are superior adhesion, corrosion protection, and when used underneath filler the ability to "lock down" the repair.
 
Barry might be biased but the guy who did this youtube video has no stake in the game. He starts with a demonstration of the issue of acid (ospho) under SPI epoxy that Barry has warned about over and over. As we all expect, SPI epoxy fails the test. At 6:15 in the video he does the same torture test on properly applied SPI epoxy. Anyone who believes etch primer is better than SPI epoxy needs to try this test on their sample.

 
The use of self-etch primer can still be found in paint manufacturers tech manuals for production (not maximum quality) work, for a couple reasons: Self-etch is easy to use, and is tolerant of poorly prepared metal. Self-etch gives at least some adhesion of coatings to bare metal, which is better than nothing at all.

Problems with self-etch include:

It remains reversible forever, so that subsequent coatings can always soak into and loosen it. SPI epoxy is not reversible, once cured, solvent will not affect it.

It's not safe to put filler over any panel that has had self-etch, even if there is a layer of other primer in-between, because the fresh filler can penetrate and loosen the self-etch, causing it to fail. SPI epoxy is specifically designed to be applied under filler, not so much for adhesion (filler sticks well to metal) but for corrosion protection. Filler and etch primer are both porous, epoxy is not, so epoxy provides a moisture barrier right at the metal where it's needed the most.

Self-etch is not water resistant, so any place the paint might become chipped or damaged can provide a path to the metal and therefore cause corrosion, since etch primer is no protection against moisture. SPI epoxy is waterproof, and in fact can be used in immersed applications once cured.
 
I really believe its just common sense for someone that don't understand paint to assume etch is best, just by the name.
To correct old school is etch, not epoxy.

Etch anything you want and let set inside for week, year?? and wash it off with urethane reducer, try it the next day with just a decent epoxy.
What solvents would a 2k primer have? Same as in urethane reducers. and can melt the etch.

Comes down to this, doing insurance work etch is all they have time to use or direct to metal urethane primer.
NO big deal last survey done showed 97.7 % of the people that wrecked their cars did not own in 3 years.

People who pay big bucks to restore their cars keep them many years.

I stopped making etch 7 or 9 years ago as keep me awake at night but most etch blow ups come at the 4-6 year mark.
Little pin heads full of a yellow solvent and blow on it and it goes to the metal rusting. (etch holds air and solvents)

Sorry, my heart is not in this conversation.
 
Although I would not use this on a lawn mower and could care less about acid etch, forget what I think how do we make the stuff and you decide???!!

Part A;
Thinned down lacquer primer, sums it up the best.
Part B:
Activator? {people think so)
Sorry, lacquer thinner with usually around 1% acid added.

You decide if this should be used under a urethane. It did work good in the 60's and 70"s.
 
Here's my take. I've used a S-W etch prime on show cars since the 80s. Never had a failure of any kind ever. Now for the rest of my story. We're in the process of changing over to Epoxy. :) ~BOB
 
Bob Heine said:
Barry might be biased but the guy who did this youtube video has no stake in the game. He starts with a demonstration of the issue of acid (ospho) under SPI epoxy that Barry has warned about over and over. As we all expect, SPI epoxy fails the test. At 6:15 in the video he does the same torture test on properly applied SPI epoxy. Anyone who believes etch primer is better than SPI epoxy needs to try this test on their sample.

Click to expand...

Did not know the guy until after video was posted and I wish he would have done one more test.
Grind one panel with 24 grinder and apply even coat of filler over the metal.
Then another panel with epoxy apply filler at same thickness .
Next day bend both panels in half, the epoxy will give filler flex and adhesion and the non epoxied panel the filler will crack right away.
 
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