How can I prevent/reverse flash rust?

Mike CA · Nov 29, 2009

I'm going to take my manifold out of the electrolysis tank today. Last time I did it started to rust. On the other parts I've done, I've run them over the wire wheel and they've been fine. I won't be able to get the wheel over the whole manifold, and there will be rust on it when it dries.

What can I do?

ScottyHOMeY · Nov 29, 2009

I use a phosphoric acid solution. It's watery and brushes right on. Depending how rough it is and how long it will be until you do something else with it, you can rinse it off after a bit, or leave it to dry. Basically it converts the iron oxide to iron phosphate which is much more stable -- same concept as bluing on a gun. Just keep any dripping away from your garage floor or any other concrete you value.

For brands, Ospho is well known. I've also found a brand called Jasco. It may take a little hunting or (Forfend!!) asking, but you should be able to find one or the other at a Lowes or HD.

mattofvinings · Nov 29, 2009

Couple things...put in welding rod oven, the low dry electric heat should drive off any moisture.

Also you could douse it with something like LPS2, LPS3 or Boeshield. Motor oil is also a possibility. If it is to be painted you can solvent-clean it back to good condition.

ScottyHOMeY · Nov 29, 2009

I really like the stuff. It's great on iron or sheet metal to get ahead of flash rust, and provides a good stable surface if something has to sit for a while before you get back to it. Scuff the surface with a little Scotchbrite and wipe down well to get the dust, and it's pretty much ready for priming and painting.

The only other caution (other than keeping it away from concrete) is specific to a part like your manifold. That is to separate the male and female sides of any threads, or of any moving/rotating parts if you can before treating. At the very least, take them apart before treatment or move them periodically an hour or so after the stuff has dried some and keep that up until it is thoroughly dry. It's thin enough that it will find its way into mated threads or moving joints, and the chemical reaction will have the same effect as the rust that causes threads and joints to stick in the first place.

Dave H (MI) · Nov 29, 2009

I don't have a lot of luck with ovens but the stuff Scotty is talking about is good. I got mine at an auto paint store but I think any high end automotive supply will have it if they sell paint.

CNKS · Nov 29, 2009

Drying it off with a towel will stop most of it. You don't need as strong a H3PO4 solution as ospho. Go to Home Depot and and get a product called "Must For Rust". It is a mild phosphoric acid solution that should be mostly used as a rust protectant. Comes in a squirt bottle, spray it on and wipe the excess off. A similar product (internet only) is Picklex 20, costs much more and I consider it no better than Must For Rust. On your manifold it won't make much difference, but I don't like using acid on cast--it can get in the pores and cause lifting of the paint later. However, I have done it without problems, but I don't use it on cast any more. The main way to prevent rust is to get the thing dry and keep it that way.

ScottyHOMeY · Nov 29, 2009

You make a good point about rough pieces. I haven't seen any pics of Mike's manifold since it came out of the tank. It looked not-too-bad before it went in, so he may have a pretty good surface going.

Where he's starting from being pretty clean, the Must For Rust (Never heard of it, but there are a lot of things I haven't heard of!) sounds perfectly adequate. Any mild phosphoric acid solution will do what I'm talking about.

What I would urge him to stay away from is a product like the aerosol PermaTex Extend Rust Treatment. It's basically a clearcoat with an acid of some sort in it to convert the rust, but leaves a clearcoat in place that, depending on what one put over it for paint on a part that doesn't get hot, might make for the lifting and peeling you describe, but will definitely do it on a manifold.

Whatever name-brand product he winds up with, I think the plain acid solution of whatever strength will do what he wants (stop the rust and stabilize the surface) and leaves his options open for when he goes to finish it, whether that be plain old stoveblack or a paint that's made for the heat it will see.

CNKS · Nov 29, 2009

Actually, I don't use anything on a routine basis any more. We have low humidity, and other than a bare surface getting flash rust immediately if wet outside, I don't get any rust -- have stored bare piecies for months inside. That probably won't work in a humid climate.

GordoSD · Nov 29, 2009

Blow dry with the air gun when it comes out. Then smooth up the outer facing visible portions with a 120 grit flap wheel on your angle grinder.
Then spray it with the Cast Blast we discussed.
If you don't have these items you shouldn't have put it in the tank. But you can spray it with WD-40, and then take that off later.
You have to think ahead when you launch off into a new project. That's your greatest misgiving in this restoration. You are good at tearing it apart, but not ready to finish the step. You have about ten half done items baking right now.

Gordo

charles todd · Nov 30, 2009

OSPHO is my poison of choice!

CT

How can I prevent/reverse flash rust?

Mike CA

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ScottyHOMeY

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mattofvinings

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ScottyHOMeY

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Dave H (MI)

Well-known Member

CNKS

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ScottyHOMeY

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CNKS

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GordoSD

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charles todd

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