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Old 03-21-2005, 06:26 PM
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Epoxy -vs- Etching primer over bare metal?

I've always used etching primer followed by a k2 serfacer over bare metal, but I have noticed more people are using epoxy followed by k2 over bare metal.......So which is better and why?


What are the pro's and con's of using either or?
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Old 03-21-2005, 07:04 PM
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Self etch primers don't require surface texture for good adhesion where epoxies will need some texture. Self etch primers are forever soluable where epoxies once cured are not. Polyester products can be applied over epoxy but not over self etch. Epoxy primers are an excellent sovent barrier once cured. Epoxy primers are more durable. Self etch primers will offer better adhesion over smooth metals but are sometimes not recomended for sandblasted surfaces.

I've done many repairs with both types of products over the years and have seen better results with epoxy primers. The epoxy adheres to properly prepped surfaces well enough that I see no reason to use any etch type primers. Epoxy makes an excellent base for applying bodyfillers.

Self etch type primers are more forgiving when it comes to surface prep. Epoxy primers need a completely clean surface with the proper texture for optimum adhesion. If there is an adhsion problem with epoxy it is usually because the surface wasn't completely clean of the surface was to smooth IMO.

There will be arguments made for both products and people have been doing quality work for years with both. I like epoxy. ramble, ramble,
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Old 03-21-2005, 07:09 PM
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Thanks bob

and I got simulare answers after doing a quick search........I gues I should have looked befor posting........sorry my bad


On the next bare metal work I do, I'll try out the epoxy to get used to it, as it seems like thats the better way to go.
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Old 03-21-2005, 07:18 PM
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Just make sure the surface of the metal is sanded good then clean it really good. When you can wipe a clean white cloth on the surface and it doesn't discolor the rag you'll be ready for primer.
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Old 03-21-2005, 08:32 PM
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Would a sandblasting with AL-OX 46 grit give enough "tooth" for SPI epoxy to adhere well?

TIA!

Russ
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Old 03-21-2005, 08:42 PM
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Quote:
Originally Posted by baddbob
Polyester products can be applied over epoxy but not over self etch.
Bob, maybe Barry can reflect on this. I was under the impression etch couldn't be applied before Polyester primer. Well, this is true, SOME polyester primers have strick warnings in bold print on the tech sheets NOT to apply it over etch primer. Then I bought some PCL polyprime, they recommend etch primer. Now,Evercoats new Feather Fill "G2" has a recommendation for etch primer.

Brian
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Old 03-22-2005, 05:35 AM
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I haven't tried the PCL primer yet but I did do some texting on a beater truck with the 2G over self etch and it worked OK. The 2G did take a considerably longer amount of time to cure though. I'm sure some of the solvents in the polyester get absorbed by the self etch then later come back out causing the slow dry time. These are the only two polyester products I have heard of that are suggested for use over self etch primers.
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Old 03-22-2005, 08:47 AM
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It was stated for years not to use polyester over acid etch.
The reason is polyester is loaded with acetone and acetone will melt the acid etch. (vinyl acetate).
Well one company, said OK for sales advantage and now they all have to.
they have nothing to lose as there is no warranty with polyester primers anyway.

This has all been beat to death in past, so if you have an inclination to use acid etch do this test yourself.
Spray some acid etch on scrap panel and let dry as long as you want, take a rag and just dip into 2K primer and wipe the acid-etch panel and see what happens. (it will melt it and wash it right off)

Also the reason the primer on your beater truck dried slow is because the melted the acid etch and the solvents got in the primer. This will show up as pinhead bubbles and than bigger ones down the road. The metal is rusting as we speak because of the solvents and air trapped under the primer.
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