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#529277 - Thu Apr 16 2009 10:22 PM Phosphoric acid neutralizing
Dan B. Offline
Wrench Fetcher
Registered: Sat Mar 07 2009 08:08 PM
Posts: 72
Loc: Texas
I have been using phosphoric acid to treat most of the paintable surfaces on my 3100. Just ordered epoxy primer and am having second thoughts about shooting over the acid prepped metal. I read the whole thread about "phosphoric acid rules" but not much mentioned about whether it needs to be neutralized with anything before priming. This first step is obviously critical. Anyone with long term experience with this stuff?

#529296 - Thu Apr 16 2009 10:45 PM Re: Phosphoric acid neutralizing [Re: Dan B.]
Flxible Offline
Registered: Sun Feb 03 2002 12:00 PM
Posts: 16409
Loc: north of the 49th
I haven't found it cause any problems, it's great metal prep for rust prevention, but also best practice when starting to shoot paint is to wipe down with a grease/wax remover immediately beforehand

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#529321 - Thu Apr 16 2009 11:44 PM Re: Phosphoric acid neutralizing [Re: Flxible]
Slickriffs Offline
Shop Shark
Registered: Tue Jan 02 2007 12:00 PM
Posts: 748
Loc: Fairfield CT
Yup-pretty standard series of events here-Never had a problem.

#529398 - Fri Apr 17 2009 09:09 AM Re: Phosphoric acid neutralizing [Re: Slickriffs]
Tiny Online
Registered: Sat Aug 06 2005 12:00 PM
Posts: 10819
Loc: South Central Kansas
If neutralizing it will make you feel better a simple baking soda/water solution will kill any residue.
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#529405 - Fri Apr 17 2009 09:35 AM Re: Phosphoric acid neutralizing [Re: Tiny]
sclor Offline
Wrench Fetcher
Registered: Mon Jan 08 2007 12:00 PM
Posts: 104
Loc: New Orleans
I use Ospho in a spray bottle, scuff with a scuff pad, then wipe with a paper towel. When I am ready to prime, I scuff with a scuff pad, then wipe with Wax and Grease remover. I have never had any problems.

The one caveat is that you can only apply phospohric acid once. Thus you have to be sure that the primer you are using doesn't also contain the acid. That means no etch primer and no hybrid epoxies that contain acid. I use Kirker Enduro that doesn't. I believe Valspar/House of Kolor is one that does contain acid. It is best to look at the manufacturers data sheets for the primer you are using to ensure that metal etched with phosphoric acid is a suitable substrate for the primer.

I hope this is helpful.
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#529457 - Fri Apr 17 2009 02:19 PM Re: Phosphoric acid neutralizing [Re: sclor]
Spotbiltxo Offline
Shop Shark
Registered: Fri Jun 06 2008 11:34 PM
Posts: 893
Loc: San Antonio, Texas, USA
Steve makes a good point, but I wouldn't expect acid-acid reaction with a previously treated surface that is totally dry.
Once the phosphoric acid reacts with the rust to form oxide then the acid has been altered. Significant reaction would occur if the organic acids are viscueous.

As a note, it is always prudent to neutralize any surface treated with acid with fresh water. Most of the directions on a bottle of phosphoric acid reccomend this step in their directions section.

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#529507 - Fri Apr 17 2009 06:00 PM Re: Phosphoric acid neutralizing [Re: Spotbiltxo]
Jimmie D Offline
Shop Shark
Registered: Mon Feb 20 2006 12:00 PM
Posts: 548
Loc: Grand Junction, Colo.
Here is what Wikipedia had on the subject.
Rust removal
Phosphoric acid may be used by direct application to rusted iron, steel tools, or surfaces to convert iron(III) oxide (rust) to a water-soluble phosphate compound. It is usually available as a greenish liquid, suitable for dipping (acid bath), but is more generally used as a component in a gel, commonly called naval jelly. As a thick gel, it may be applied to sloping, vertical, or even overhead surfaces. Care must be taken to avoid acid burns of the skin and especially the eyes, but the residue is easily diluted with water. When sufficiently diluted, it can even be nutritious to plant life, containing the essential nutrients phosphorus and iron. It is sometimes sold under other names, such as "rust remover" or "rust killer." It should not be directly introduced into surface water such as creeks or into drains, however. After treatment, the reddish-brown iron oxide will be converted to a black iron phosphate compound coating that may be scrubbed off. Multiple applications of phosphoric acid may be required to remove all rust. The resultant black compound can provide further corrosion resistance (such protection is somewhat provided by the superficially similar Parkerizing and blued electrochemical conversion coating processes). After application and removal of rust using phosphoric acid compounds, the metal should be oiled (if to be used bare, as in a tool) or appropriately painted, by using a multiple coat process of primer, intermediate, and finish coats.

#530138 - Sun Apr 19 2009 07:22 PM Re: Phosphoric acid neutralizing [Re: Jimmie D]
50adrod Offline
Wrench Fetcher
Registered: Sun Dec 30 2007 10:13 PM
Posts: 196
Loc: Louisiana
I use SPI epoxy and they advise against it. they recomend sanded bare metal only. if you are using SPI epoxy just give Barry a call, he will help you out.
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