What to spray onto metel immeditely after removing rust?

[JD4430]

I am a beginner but plan to use electrolysis to remove rust on some of my parts. Once that step is completed, can I simply just spray some primer on the part to prevent further rust until I paint it at some later date?

[J Franklin]

Look up the product OSPHO. It is the best I have found to inhibit flash rust.

[JD4430]

Thankyou J Franklin.

[ursus]

Originally Posted by J Franklin

Look up the product OSPHO. It is the best I have found to inhibit flash rust.

Exactly! I haven't found anything better, provided you don't leave the treated material exposed to rain or ocean spray.

[Joe K]

Electrolysis works well to "convert" rust. But it converts red-rust - which can't be painted over - to black rust which can.

I don't have the chemical formula of the various rusts in front of me.

Many who do electrolysis will follow up with some sort of mechanical removal for the black rust. Generally it remains in pits and hollars and can still be a good foundation for paint - but it will be better and possibly more dimensionally true, if the black rust is removed with a quick bead-blast, wire brush, or even scotchbrite pad.

THEN one would do best to do a phosphate treatment by its various names. Ospho was mentioned, but I've used Phosphoric Acid Kleen-Strip "Prep & etch" which used to be sold under that name but now is sold under "concrete/metal prep." All of these are similar with Phosphoric Acid as a constituent.

Curiously, the Kleen-Strip product recommends a dilute (with water) application of their product. I use about 50-50 with warm water. And then finish up after an hour or two "sit wet" with another warm soapy water wash.

A gas is generated during phosphate application to the metal. Quite suffocating I suspect this is not good for one's lungs so you maybe best do this phosphoric acid step outdoors - or at least in a well ventilated area.

I have commented previously that electrolytic rust removal does a PERFECT job of converting rust for painting. Chemical perfection that is. The problem is it also offers afterwards a perfect "landing place" for chemical atmospheric oxygen to land and re-start the rusting process. Think of all those chemical bonds of iron just waiting for an oxygen molecule to come by so it can revert it to iron mine tailings.

It is considered by some that bead or grit blasting "covers" in mechanical impact these bonding sites. Similarly, Phosphoric Acid chemically fills them, and may fill them better working on the atomic level as it does.

One of the larger pieces I have cleaned electrolytically is a Worthington Steam Pump of smaller size. It sat in the bath for a week or so and I periodically changed location of the electrodes and added chemical to the bath. As it came out of the bath, I washed everything with hot water in a tub. THEN I applied Prep & Etch. And after sitting a few hours wet, then washed again with warm soapy water.

That pump body was not a high priority - so I let it sit in my shop - for over a year before it was painted. The shop is dehumidified in the summer, but otherwise the pump was not protected until it was painted. I could not detect any rusting to red rust and little change in appearance. It's now painted.

Right now I have a Model A wheel which was electrolytically cleaned, and then Phosphoric Acid treated. It's a black to dull grey in appearance now six months later. No red rust. I should get back to that before I lose ground.


Joe K

[40-A Twins]

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My electrolysis tank is a garbage bin large enough to submerge over half a front fender. The more anodes you can fit in the tank and the closer they are positioned to the rusty part, the better it works. I made a bunch of jumper wires with alligator clips to connect anodes to the battery charger. Any scrap steel will work as anode. Also burned up the diodes in the battery charger from running it at the highest setting too much, so now use the lower amperage settings. The diodes were not hard to replace. The door in this photo was cooked overnight, when the tank was half empty, and the rust came off with minimal scrubbing with a scotchbrite pad and water.

[ModelA29]

2 part epoxy primers are best. Regular primer works if you'll be finish painting in a short time. Regular is actually porous and allows moisture to reach the steel.
The epoxy primer acts as a sealer too so it prevents the moisture from creating more rust. Eastwood has 2 part epoxy in a spray can but it's pricey.

[kenparker0703]

back to the OSPHO. i get it at the local hardware store. Somewhere between 25-30 $ a gallon. Gallon goes a loooooong way. If spraying wear a respirator. U dont wanna breathe those spray fumes. I brush it on with a cheap HF 1 inch brush. Then with gloves on wipe the excess off with a rag or heavy duty paper shop towel. Let it sit for 24 to 48 hours - takes that long to fully dry. Once dry wire brush the iron oxide grains off.



Ospho is diluted version of Phosphoric acid. Read the ingrediants of your Coke. The acid turns the red oxide (rust) into iron oxide - dark grey and somewhat rough.


Before paint or prime the roughness will need to be wire brushed of or sanded. ken

[Synchro909]

Back when I was a kid in my teens, I needed a bicycle to get to school. My father gave me his old one and I set to getting it going again. The bracket he had made for the headlight was rusty and I wanted everything to be "just so". Dad gave me a bottle of phosphoric acid and told me to soak the bracket in it till the morning. It came out as clean as a whistle and when it dried, there was a white powdery residue on it. Dad told me to leave it like that and I'd have no problem. It was and there was no sign of rust on it for about 15 years.
I've never heard of Ospho (probably not available here) but if it is diluted version of what I used, it should be OKish but a more concentrated version might be better.

[Bob Bidonde]

I sprayed bare body metal with an epoxy primer. On mechanical parts is used POR-15 Chassis Black and eventually an overcoat of Krylon Black.

[rotorwrench]

The phosphoric conversion coatings are a mix of proprietary materials most of which is water for dilution of the phosphoric acid and some zinc salts to add a bit more protection. They also put a resin material that helps keep the wet portions on the treated surface. Ospho is a trade name and it is designed to be a pre treatment for structural steel prior to further priming or painting. It works better for a basic conversion coating if diluted.

Phosphoric acid converts the non inert iron oxide into the black iron phosphate which is inert. A person can use Gibbs or Boeshield spray products for short term protection but it has to cleaned off thoroughly prior to priming and painting.

[brokenspoke]

Gibbs is a good product

[BillLee/Chandler, TX]

I saw: fellow Model A guy keeps a garden sprayer with diluted Ospho in it. When he cleans up a rusted part he sprays a thin coat on and lets it dry. Rust: zero after years of sitting in the corner of the shop.


I have a windshield frame that I some day may use. I cleaned it up several years ago using all sorts of methods: elbow grease, Rust911, Ospho, etc. Last was Ospho. It has been just 'sitting around' for over 5 years and there is no rust on it now.

[Oldbluoval]

Bill Lee
Yes I often do the same.
Also, if you prime with epoxy and have to do subsequent body work, the stuff can be the dickens to get off. Especially, if shrinking involved. The Ospho is much easier to work on top of and a great product.

[tin man]

rust 911 works very well!

[JD4430]

Thanks to all of you for so kindly responding to my question.

[Rusty30roadster]

I use pb blaster30wt engine oil, or wd40 after rust removal.

I have a 100 gal e-tank and just ran 4 trans cases and an f100 steering box through it. Flash rusting is a real problem in southern ca because parts seem to dry and rust instantly. Stromberg carb bases are my nemesis when it comes to flash rusting. After a run, I always rinse with the hose really well, dry as much as I can with a towel and spray with pb blaster or wd40 is my 2nd choice. When I get around to painting, I will wipe the oils off with acetone or alcohol and primer with vht high temp engine paint. It contains acrylics and dries super fast.

When I’m out of spray products, I use 30wt engine oil to prevent rust. Apply with a rag.


My advice, don’t over think it or buy more unnecessary products. Slap what you got on there and it’s usually fine as long as you remove it before painting.