phosphoric acid?

[cajunz]

Hey guys, I'm pretty new to the sight but love all the great info you guys provide. I hear you talk alot about using phosphoric acid to kill rust. What exactly is the proceedure for using this stuff. I have a '78 280 completely stripped for rust repair in the rear 1/4's, doglegs, floor pans, and front frame rails. Do you have to neutralize the acid after using it. I have never used the stuff before. Any info would be greatly appreciated.

Brent

[DeesZ]

Phosphoric acid, if I recall correctly, is an active ingredient in navel jelly. It can also be purchased in various states of dilution at places like NAPA, etc. sold as aluminum brightner, etc. Navel jelly works well, but slowly, for removing rust, not 'converting' it to something else (as claimed by POR15 and other like products). So, depending on your definition of "kill rust", this may or may not be what you are looking for. And, yes, it is recommended that the acid be thoroughly washed away & neutralized prior to applying anything to the surface of the metal.

[xray]

Iron oxide is converted (reduced, IIRC) to water and iron phosphate (blackish residue) after exposure to phosphoric acid. I typically leave the acid on the rusty surface for about 30 minutes, then rinsed and dried (heat gun works well). Iron phosphate is a poor rust preventer as it doesn't adhere well, so it's advised to prime and paint as soon as possible.

Check some chemistry websites or google it to confirm.

[hls30.com]

I keep the rusted area wet, and wait until I have a uniform dull gray finish-where the rust has pitted the metal the process will result in black specs in the pits, using a stainless brush I aggitate the pitted area until the specs are gone. Even in our South Georgia humidity, I have found PORs Metal ready and Ospho to be good rust inhibitors for several weeks when treated this way and placed out of the weather-if you question the protection, a simple second treatment gives peace of mind.

Both leave a zinc phosphate coating on the metal if allowed to dry, I wipe the phosphate off with a cloth saturated with Laquer thinner..

BTW, I treat all sand blasted metal to the same treatment-blasting rust into the pores of the metal is not good for keeping rust gone, but followed by an acid bath, the rust does not stand a chance.

Will

[JimmyZ]

http://warbuddies.homestead.com/RestoHelp.html

A site I made for just these kind of questions

Jim

[Zs-ondabrain]

And even easier is the SEM Rust converter. Clean up the rust as well as possible (wire brush, grinder, what have you) apply with a brush or even a touch up gun (paint gun) Let it dry then do the bodywork. or Even apply it on any questionable areas.

You don't wash it off when you're done and it only takes a light film. Little goes a long way and you can spray it up into cavities and call it done.

Dave.

[Carl Beck]

Just to make sure it is clear:

Oshop is a brand name - it can be purchased in quarts or gallons at most Auto Body Paint Suppliers. I believe I've seen it at some of the Auto Parts Suppliers as well.

Ospho is a diluted phosphoric acid solution (about 12% as I recall), ready to use right out of the container (you don't want to use straight phosphoric acid!!). Ospho is environmentally friendly - if washed down/diluted with lots of water (phosphate is used as a fertilizer).

As Steve and others mentioned - if you apply a phosphoric acid solution to iron oxide, the iron oxide is chemically converted to iron phosphate, which is stable. The US Military has been using phosphoric acid solutions for 60+ years to control rust, and they have done extensive testing of thousands of products. The truth is they haven't found anything more effective at killing rust on metal surfaces. Also as mentioned, it prevents flash rust from forming for a brief period (days to a week or so in humid climates).

I've been using Ospho for decades, it can be sprayed, brushed or poured on effected area's - if removed with water within a few minutes - it won't damage painted surfaces surrounding the rusted area.

FWIW,

Carl B.

[webdawg1]

Saw this product the other day while tooling around on the net...Pretty much along the same lines as the chemical you mentioned, but this product is more of a short term/long term metal protection to keep "flash rust" at bay...while you work on other areas of the car and are not quite ready to paint just yet...

http://zero-rust.com/zero-rust-prep-step.html

webdawg1

[26th-Z]

Directions on how to use OSPHO from OSPHO. http://www.ospho.com/directions.htm

Do a web search on rust repair and use of phosphoric acids. We have been over this topic a million times. Use the search function on this site.

[cajunz]

thanks for the quick replies. You guys are a wealth of good information. If I understand correctly, you wash the phosphoric acid off with water and then dry thoroughly? Again thanks for all the help.

Brent

[Nissanman]

After you let the product do its' thing, you wash it off with clean water.

This cleans the surface but more importantly, neutralizes the remaining acid.

The surface then can be a dull gray to a light yellow/straw in colour.

Wipe it immediately with a swag of paper towels to mop up excess moisture.

Then wipe it again with more towels but this time, spray the surface liberally with methylated spirits.

A hand held pump pack is great for this, one you can vary the nozzle from a spray to a stream.

The metho. will displace any remaining moisture from seams, cracks, nooks and your actual cranny as well.

You can then use de-humidified compressed air to ensure the panel is super dry.

Concentrate on the seams etc. to blow out any trapped fluid.

The panel is then ready for wiping down with "Silicon Off" or "Prepsol", to make it primer ready:)

[JimmyZ]

thanks for the quick replies. You guys are a wealth of good information. If I understand correctly, you wash the phosphoric acid off with water and then dry thoroughly? Again thanks for all the help.

Brent

You don't wash ospho off with water. There are other solutions (various "metal preps") such as PPG's DX 520 which are rinse off and dry types. These don't do as thorough a job as an ospho type of solution where you leave it on and have the acid "attack" the rust. To me, ospho is the king of rust killers. The metal prep types are meant for treating any flash rust (light stuff) which happens once the metal is exposed for a short time. Ospho tackles the deeper/thicker rust which has been festering. It's always best to remove as much rust as you can before applying.

I like to ospho then remove the ospho scale or skin with a metal prep such as DX520. The problem with leaving ospho on underneath is that it can be too thick in places which creates a shifting substrate. A thin layer of ospho left over would be OK. (This is in the directions) My body shop had a paint job come back to him because something went wrong with the ospho. (Hence my suggestion of completely removing the stuff) Ospho needs to be sanded flat or removed because it will show up in the finish coat as streaks and bumps. (If you lightly scotch brite it)

The reason I like the idea of using a metal prep as an aid in ospho removal is that you completely remove the ospho film by using a scotch brite pad while keeping the metal under a mild acid bath. (Use gloves or have your hand eaten! )Let's say that you were to sand through to bare metal suing a dry method and some stray moisture were to get on the exposed stuff. You would end up with rust under your paint. It's overkill but it's better than completely stripping a car the second time because you didn't control rust.

My 2c

Jim