What's the proper way of using phosphoric acid? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-08-2006, 06:35 PM
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What's the proper way of using phosphoric acid?

Every time I use phosphoric acid to etch panels, the metal flash rusts when I rinse the acid off. Today I used a POR-15 tank sealing kit for a motorcycle tank that a customer brought me. Included in the kit is a bottle of phosphoric acid to etch the inside of the tank. After sloshing this stuff around for 30 minutes, I rinsed the inside of the tank with clean water 3-4 times as the instructions told me to do, but now that the tank is dry, there is a fine coating flash rust inside. This is a pain in the ***** !!! What's the secret?? Thanks, Dan
www.geocities.com/dantechfab

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Old 02-08-2006, 07:10 PM
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My instructions for OSPHO (phosphoric acid) say to coat the part and let it dry, nothing about a rinse. I did this and was not happy with the results. However, I used a spray bottle and misted it on my body panels instead of using a brush. It dried in rivulets, where the OSPHO was heavier, I now have black powdery buildup that will need resanding before priming.

Russ
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Old 02-08-2006, 07:59 PM
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my past experiences with ospho is that if there is black, there is still rust. i normally sand the coating off, then recoat using a squirt bottle(misted on heavily) then let it drip off when it is all gray, then it is ok. that is when you can coat it, but i normally sand it off then paint with an etch primer.

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Old 02-08-2006, 09:07 PM
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I have to disagree!! Under no circumstances should you ever put an etch primer over a panel that has been already etched with phosphoric acid. IT WILL PEEL !!
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Old 02-08-2006, 10:40 PM
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Quote:
What's the proper way of using phosphoric acid?
Why, you drink it, of course?

(check the label on Coke and Pepsi)
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Old 02-09-2006, 08:18 AM
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Hmmmm!! Not quite the response I was looking for!
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Old 02-09-2006, 08:50 AM
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I purchased Oxisolv from Eastwood, which they say is Phosphoric Acid, and the instructions said to use Thinner (or Eastwood PREP) to clean before painting-
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Old 02-09-2006, 10:50 AM
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In my opinion, acid metal treatments need to be washed off with water unless the instructions specifically say not to. Flash rusting is not nice, but I've never seen it cause a real problem. What I've seen as a good practice is to follow the acid etch with a product like PPG's DX520, which will produce a very thin zinc phosphate coating and prevent any flash rusting of the steel long enough to apply primer. The zinc is also sacrificial, so it will help reduce corrosion in places where the metal may become exposed, like stone chips.
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Old 02-09-2006, 03:19 PM
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Quote:
Originally Posted by crashtech
Flash rusting is not nice, but I've never seen it cause a real problem.
Remember, you said this not me!

I would never bring this up on my own, just like I won't bring up I sand blast everything and do not warp panels.

Since you brought this up back in 95-97 I got a scrap fender and sandblasted it. Washed it with wax and grease remover than rinsed with the hose and dried.
I let the fender set two days to get a good yellow haze I applied two coats of epoxy and than shot two coats of centari over the epoxy.
The fender is still on the roof and the paint is all bleached out but there is no rusting or popping from rust starting.

How I do frames, is sandblast than with a pressure washer I use waterborne wax and grease remover and blast the frame when done rise with a hose blow dry and next day epoxy. Like you never have had any reaction from flash rusting.

What I also did around 2000 is I duck taped 3/4 of that fender and did a chip test on the exposed part, even then it passed with no problems.
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Old 02-09-2006, 05:20 PM
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Quote:
Originally Posted by BarryK
Remember, you said this not me!
It seems strange to me that you are unwilling to assert your opinion on certain things. You seem to me as one of the most self-assured people on this board (especially now that you-know-who is banned, lol).

I'm not afraid to offer that opinion on flash rust. I'll go even further and say that flash rusting indicates that the metal is exceptionally clean and ready to accept whatever is to be put on it. BUT, for those who just can't accept that, a zinc phosphate treatment is beneficial though it adds cost and an extra step.
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Old 02-09-2006, 05:33 PM
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I think we agree as my feeling is cleaner is more important than a flash rust.

Now I will say this on the outside of the body If it was to flash I will buzz it with an 80 grit real quick.

As far as posting, I think its good for someone to question you if they disagree or don't understand. This then allows you to get deeper and bring up other points. Problem is a statements like it makes no difference and no facts so why bother. In my old age I would just as soon walk away and not explain. I'm getting better at ignoring.
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Old 02-09-2006, 09:06 PM
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Usually a quick rub with a red scotchbrite will remove any flash rust before you apply the primer, no big deal.
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Old 02-09-2006, 09:16 PM
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WELL,
Being that IT is a POR 15 kit, Ain't that stuff SUPPOSED to used over a "slightly" rusty surface?
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Old 02-10-2006, 10:38 AM
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Quote:
Originally Posted by crashtech
Why, you drink it, of course?

(check the label on Coke and Pepsi)
when i first saw the post i thought the same thing....
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Old 02-10-2006, 02:01 PM
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Quote:
Originally Posted by Bee4Me
WELL,
Being that IT is a POR 15 kit, Ain't that stuff SUPPOSED to used over a "slightly" rusty surface?
yeah, disreguard that my last post, wasn't thinkin POR for some reason. light rust is good for POR adhesion so they say.
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