The Stovebolt Site Forums The Shop Area Paint and Body Shop Phosphoric acid neutralizing

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?

Thanks

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

Bill

Yup-pretty standard series of events here-Never had a problem.

Keith

If neutralizing it will make you feel better a simple baking soda/water solution will kill any residue.

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.
Regards,
Steve
New Orleans

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.

Spot

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.

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.