The Stovebolt Site Forums The Shop Area Paint and Body Shop How to Apply Acid Etch before Priming

Howdy,

Read a few methods from other posts, but nothing too fancy.

I live on the coast and have a heck of a time trying to get my stuff primed before it flash rusts. So I've been etching with phosphoric acid but its a pain in the butt to clean off the dried residue by sanding or wire wheeling before I lay down the primer.

The other way I haven't tried yet is to wipe off the excess with a towel before it dries.

Any advice on diluting it before hand, or maybe neutralizing it afterward? Any tips on the application part; spray, brush, wipe off, etc.?
I've sprayed a baking soda solution on but that was just as messy.

I would always wipe it off before it dries. You'll have much better luck that way.

An even better system is to sand or sandblast the panel to metal, clean it with PRE and just shoot epoxy primer. That allows you to skip the acid etch step. You can then do body work on top of the epoxy and it won't rust. I even would spray panels that I knew I would be doing dolly/hammer work, cutting, etc. It was just easier to sand and respray over the worked areas than to deal with a completely rusted panel.

x2 on the epoxy

I had good luck letting the phosphoric acid to dry over night after applying it thick with a brush and stirring it around with the brush a couple of times in the first few minutes. I then came back the next day with more phosphoric acid which loosened everything up and wiped it off right away leaving a thin layer. This produced a nice fairly uniform gray layer that I applied epoxy primer to after it dried for a few days. No sanding needed. This worked very well for me. I agree that media blasting followed by epoxy is probably a better way to go if that works for you.

I couldn't deal with having to metal work and primer all the parts at once so I did them one panel at a time using the phosphoric acid to keep them in good shape until primered but more importantly, to get to any rust in areas I could not see or get some kind of tool into.

Main problems I have is I both live on the coast where things will devour even a nice blasted part quickly sprayed with epoxy, and I also use beach sand which has a lot of salt in it already. I blasted and epoxied my wheels and they've held up pretty well so far (garaged) but the epoxy I'm using just didn't seem to have the bite that my inner fenders did when I used a self etch primer over phosphor-etched and wire wheeled prep-work.

I'll definitely try the wipe excess route this weekend.

I live 4 miles from the beach in Florida, so I have experienced what you have stated. The reason people use etch primer is to give the metal some tooth (at least that is what I have been told). Sandblasting does the same thing. So either the metal wasn't cleaned with PRE or there is something wrong with the epoxy you used. You should have no problems with rust after spraying epoxy over a sandblasted and degreased panel. At least I have had no problems.

hello
i have encountered the same situation. i'm gonna go with the epoxy primer. it sounds like this "PRE" is an integral part of this process. what is it, and where do i get it? one other question, some rust areas that i have ground down to metal are still pitted and somewhat discolored. is it still ready to prime? or, is there a potential to re-rust.

thanx

PRE is a solvent that removes silicone and other contaminants. See here: Eastwood.com

You can get any silicone/wax remover from any auto paint store. It's cheaper too.

Not sure about the pits, but that is where the phosphoric acid helps to neutralize the rust. You could spray on the Phosphoric acid and wipe it off a few times to see if that helps. Then spray liberally with PRE. Then epoxy prime.

Fletch, if you haven't used the phosphoric acid treatment on what you describe it is possible it will continue to rust. The situation you describe is why I used phosphoric acid in the first place. If you treat with phosphoric acid any remaining rust in those pitted areas should be converted to iron phosphate instead of iron oxide and become essentially inert. Leaving any rust behind can, and many people say it will, rust again at some point.
That is one of the great advantages to media blasting- it gets all those little rust pits cleaned out.

PRE
Just another overly priced product sold by Eastwoods praying on people because they lead them to believe Eastwoods is the only source.

PRE is just a solvent based surface cleaner. PPG makes a good in DX330, priced at about 20 bucks a gallon.

As for applying epoxy primer over any type of etch product, better check your product's technical sheets!!!!!!

Most epoxy primers on the market are NOT friendly with etch primer products. Typically they attack each other and sooner or later the epoxy loses it's bond and falls off the surface.

You should have tech sheets for all the products you plan to use. Inside they will tell what you can apply over and under that product and also how to apply it...Eric

On a side note, PPG and few other paint manufacturers don't really suggest applying etch primer over media blasted parts especially sand blasted parts. If applied to thick the etch can pool in the bottom of the pits created by the sand or rust pits. This pooling of etch primer never really dries then you topcoat it with another paint sealing off this pocket of undried acid. Now you have a time bomb ticking away and rust pits building up once again...Eric

I sand down as good as possible, hit the whole thing with a good rust converter (for the pits), lightly sand again and epoxy prime. The high-build primer fills in the pits (it may take a few coats), block it down and you're done. I've been doing this for years, never had a problem. Some people overthink and overact the problems.

The recomended method is to apply epoxy primer over freshly sandblasted steel,without washing or wiping with anything.
Any liquid will be trapped in the pits and cause bubbles in the surface.

Wally Body,
I've gone straight to epoxy after sandblasting as well and have had no problems. But when I mentioned that system to a couple body guys they said the blasting still leaves dirt and residue that the cleaner can remove. So after that I started with the wax/silicone cleaner. Haven't had problems either way...so far.

sevt_chevelle is right, go to a auto paint store and buy the cleaner by the gallon, much cheaper!

All the mfgrs. paint scools I've been to say don't wash with anything after blasting.
Blow it clean w/compressed air and prime with epoxy primer.
This is the info from PPG and Dupont.

So I'm sanded down to bare metal with minimal pitting in some areas. What do I do first? I've already got some phosphoric acid in some spots. Do I need to remove those white areas or can I epoxy prime right over those? I'm worried that as fast as I'm removing rust from this truck, by the time I make my way full circle, the original parts will be rusted again!

Also, what about underneath? Don't have the money to get everything sandblasted right now, so I'm doing it all by hand, which has already taken up hours and hours and hours... worth of time. What about those parts underneath the truck? Such as the underside of the fender? There is surface rust there as well. Some kid that wandered by the garage today told me I could just get an epoxy coat primer and then put a rubberized undercoat right over that? This by no means will be a show car for me, but I don't want to do a half-a** job either. Would appreciate your input!

thanx for all the input. i'm going to purchase the phosphoric acid tomorrow. i have a paint gun, i think i will buy epoxy primer and shoot it myself. once i am done installing the patch panels in the windshield surround, lower doors, and lower cowell, (i'm new to welding too), i'll shoot it with the primer, and take it in to have the cab painted. the running boards, inner and outer fenders, and hood are all gonna be powder coated. the outside of the cab will be painted to match. i have it completely disassembled and powder coating is cheap and durable. i'm even having all the trim powder coated gloss black, (i've already had the wheels done). at this point, i'm pretty sure i'm gonna do the frame and engine compartment with the POR15. i've learned more in the past 2 months working on this truck than i have in the last 10 years. lotta fun

When you pick out the epoxy you plan to use, check out the tech sheet to see if it is indeed compatible with the phosphoric acid treatment. Some epoxies are, some are not. If they are incompatible you will not notice the issue until about six months after your paint finish is complete and your truck is sitting in the sun at a car show. The paint starts to react with the acid, small bubbles (about 1/16 diameter) show in the paint finish as delamination takes place. Just an FYI to insure the components are compatible before you begin to spray the expensive stuff.

My understanding of the phosphoric acid and epoxy problem is getting the acid neutralized. The key is reapplying the phosphor to the the panel and then washing it off with water while its still wet. I live 2 miles from the beach and don't understand what all the rust fuss is about. After applying phosphor to my bare panels and washing it off with a hose or even a pressure washer when done (while still wet or if time got in the way reapplied days later to reactivate the acid) I simply blew the panels dry with a shop vac and found I could let them sit for a week or more with no problems at all. Occasionally a very light flash rust appears but that comes off with a light sanding. I then hit the panel with a wax and grease remover let it sit for a min of 30 minutes and then spray my epoxy. The key there is making sure everything has a chance to evaporate out of the pores of the metal before sealing with the epoxy... just my .02 good luck with your project.

I agree that neutralizing the acid should take care of the issue, but many people use phosphoric acid as a shortcut to the work involved in abrasive prep (sanding, sandblasting, etc). No disrespect to anyone intended, but unfortunate to human nature, once we start with the easy way, it normally carries over to other areas, including the clean up methods you mentioned. In most instances where I have read discussion or recommendations on the paint and body forums for phosphoric acid treatments, rarely does anyone mention any side effects or compatibility issues. (where jomichael and sevt_chevelle got it started here, thanks!) Knowing these issues exist is the first step, as most people will get an online recommendation to use the stuff with no consideration of cross-component contamination, likely from someone not aware themselves. Unfortunately this can end up being a costly mistake after the more expensive topcoats have been applied.

If the manufacturer advises of a compatibility issue with their product and phosphoric acid, who's advice would you take? How do you insure without a doubt that all of the acid has been neutralized? Anyone at this stage should either search for a primer that does not have these side effects (if they plan to use acid...), or use a method of panel prep/rust removal (abrasion) that will not degrade any paint adhesion per the manufacturer's recommendation. As expensive as paint products are, not to mention the work involved, it pays to have all the information up front.