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Fri Mar 28, 2014 5:34 pm

I searched and couldn't find a specific thread pertaining to this..

I've got quite a bit of bare metal (mostly under the car's trunk area), that I've gone over with Phosphoric Acid (Etch n' Prep), then washed the entire area down with fresh water and dish soap (while scrubbing with a rag), rinsed with pressured fresh water.. I then hand dried everything with towels, then sprayed it all with hi-pressure compressed air. Now almost all of this bare metal is a weird streaky gold color. I expected it to be a bit more of a dull but bright silver. Is this irredescent gold color normal... can I finally shoot the epoxy primer on these bare areas? Thanks.

Doug C

Fri Mar 28, 2014 7:42 pm

I used a solution from KBS called rust blast which contains the phosphoric acid. It turned into the gold color with some white streaks. I used some grease and wax cleaner to wipe down the surface before spraying some ppg dp90lf epoxy. sticks really good so far.

Sat Mar 29, 2014 10:33 am

I've done a bunch of research on this topic...and can't find much about it. I do not like the brown color that the phosphoric leaves after being rinsed with water. It's the salts in the water reacting with the phosphoric acid to create iron phospate. The water usually will do no harm because you have put the acid down first. You need to avoid the water rinse. I had some issues with the brown color and what I did to get rid of it was dilute the acid with water to at least 50/50 but more like 70water/30acid. Spray it on, scrub with prep scrubby, and wipe off immediately with a clean rag. Spray and wipe until the rag wipes clean. This leaves the surface perfect. There will be some white residue in corners etc. where you can't wipe it all off with the rag, but that is the phosphoric treatment.

One of my friends said to use the wax&grease remover and a clean rag, go over the brown area with this, does the brown stuff wipe off on the rag?? Then you will have a problem with paint adhesion.

Anything that wipes off with the wax&grease remover should be totally, removed.

Sat Mar 29, 2014 5:20 pm

Thanks Guys..

I actually mixed my 'prep n etch' at 4:1.5 , I didn't wipe the surface down with wax and grease remover but I did so with Acetone and nothing came off on the rag. So I guess that's a good sign, but that was after drying, compressed air and a heat gun... so that could be why I guess.

Ian have you ever painted over the gold colored areas?

Doug C

Sun Mar 30, 2014 6:28 am

What do you guys use for a scrubby since the stuff eats the green ones?

Sun Mar 30, 2014 10:22 am

Phospohoric acid does react with the iron in your steel to form iron phosphate which is substantially more resistant to corrosion than the steel itself. The iron phosphate layer left behind acts as a passivating layer to reduce corrosion over time. However, there are other factors to consider for overall performance. Acid pre-treaments leave an acidic surface and many epoxy primers do not like an acidic surface which can cause adhesion problems. This is made worse if you have areas where the acid pretreatment is heavier so most companies recommend a good rinse or neutralization before the epoxy is applied. Before you start with your metal project it's best to follow your paint manufacturer's recommendation for metal prep given the product you are using. Many manufacturers offer a warranty without using a metal pre-treatment since the epoxy protection mechanism is very effective without it....good luck

Sun Mar 30, 2014 11:24 am

I have not tried painting over the gold/brown stuff...it sketched me out when it was wiping off on a clean rag.

volksaddict wrote: What do you guys use for a scrubby since the stuff eats the green ones?

Red primer prep scrubbys they're like $18 a box. It does eventually deteriorate the pad, but thats when you throw it away and get a new one.

Mon Mar 31, 2014 11:56 am

Glad to hear I'm not the only person that has battled this!
I had the same issue using Rustmort (same kinda thing) and also couldn't find any information, despite spending a lot of time searching. I even called tech support and couldn't get an answer.

My concern was that it was causing flash rust, so when the golden/brown color appeared I would spray a very light coat of Rustmort or Metal Ready (also contains phosphoric acid), let sit for 30min/1 hour then wiped off lightly with a damp rag.

I found the more effort I used to remove the old/dried acid, the more the color appeared. Since I've started using just a slightly damp rag and less force, I haven't had it happen again, and have had zero issues with filler or epoxy primer over top. Evercoat filler and Proform Epoxy Primer.
Hope that helps!

Mon Mar 31, 2014 1:34 pm

I found this site kinda helpful. The pics of the items after phosphating is the most helpful...so you know what to aim for.

http://www.metaltreaters.net/phosphating-chemicals.html

Quote: We also have a one shot process for degreasing, derusting & phosphating for components that could not be dipped.

That's the jam.

Mon Mar 31, 2014 2:18 pm

As some epoxy primers arent for bare metal that has been treated with phosphoric acid, will a scotch brite pad properly re-prep the metal for epoxy primer?

Mon Mar 31, 2014 4:38 pm

The stuff I have been using is Eastwood's Afterblast. The one thing they don't mention is that it will burn your skin and smells horrible. That's where the dilution comes in, and I always turn a fan on and wear crazy protective clothing when using it. I do a 1ftx1ft area at a time, spray it on, scrub with scrubby, wipe with cloth. Then I spray it on and wipe with cloth until clean, only scrub it once.

Quote: After Blast is designed to clean, degrease and etch freshly blasted or sanded metal prior to painting or powder coating. Use with a plastic spray bottle to liberally apply to the part, wipe and reapply until all contaminants are removed. The blend of aqueous cleaners and phosphoric acid properly cleans, etches the metal and leaves a zinc phosphate coating that is excellent for paint, primer or powder adhesion. Also protects the metal from flash corrosion for extended periods. Use on all your fresh cast iron, steel or aluminum components.

Maybe these links will help?

http://www.jalopyjournal.com/forum/showthread.php?t=682968

http://mustangforums.com/forum/classic-mustangs-tech/552633-phosphoric-acid-paint-question.html