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Rust treatment

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by Gordon » Tue Aug 11, 2020 3:56 pm

Hi all, can anyone recommend a treatment that will neutralise pitted rust on the floors after having used a wire brush in a grinder to clean the surfaces. I'd also like to treat the underside of the wings.
Hammerite rust treatment looks good when it turns the rust spots black but if you scrape it when dry the rust is still there !
Any ideas would be appreciated. Gordon Walton
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by johnw » Tue Aug 11, 2020 5:13 pm

I don't like rust convertor treatments, especially chemical rust remover. I am not convinced that they leave the metal in a stable state.
I prefer wire brushing, zinc rich primer, then a top coat done in such a way that you can see when this fails.

I don't have an answer, other than the suggestion to avoid rust remover/killer/convertor type products.
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by Gordon » Wed Aug 12, 2020 11:11 am

Has anyone tried a product called Scalex which is phosphoric acid based at a concentration of 45%?
Any guidance would be appreciated
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by John Staddon » Wed Aug 12, 2020 4:19 pm

I have only ever used Kurust so can't answer the last question. I can say that no matter how aggressive a wire brush in an angle grinder appears to be it doesn't get rid rust, just surface rust, rust in pitting or just deeper patches gets left behind and though the wire brushed surface may appear rust free if you go over the surface with a course flap wheel it soon turns orange with rust again. Use a flap wheel in an angle grinder and you will grind the metal down to the level of the pits and get rid of the rust as well, and of course make the metal thinner which could be a problem, in which case I have also used a burr tool in a dremel and literally bored the rust out of pitting, but it's a slow process (a needle gun is cheap and does the job much quicker but you need an air line to attach one to). Basically get rid of all visible rust first, then when you think there is no rust left treat the surface with Kurust or similar which should kill any traces of rust you can't see (otherwise rust WILL come back). All learnt the hard way when rust treating parts off Interceptor No 88.

Of course most of the de-rusting on No 88 has been done by Kestrel Classic Cars, I only tackled the parts we took off before the chassis was sent to Kestrel, like suspension and rear axle, and the product Alan at Kestrel recommends for initial coating of metal after the rust has been removed (by bead blasting for No 88) is Electrox, https://www.bilthamber.com/electrox

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by Gordon » Wed Aug 12, 2020 6:18 pm

Thanks all. I'll get a bit more information on Bilthambers products to see if their treatment will tolerate some degree of pits containing corrosion. On the underside of wings where underseal and original primer has disappeared leaving a rusted surface it's going to be very difficult to get 100% bare metal.
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by johnw » Wed Aug 12, 2020 8:38 pm

John Staddon wrote:Alan at Kestrel recommends for initial coating of metal after the rust has been removed (by bead blasting for No 88) is Electrox, https://www.bilthamber.com/electrox

John


That Electrox is a zinc based primer so it could be very good. I find that a wire wheel in an electric drill gets to the bottom of more pits than the much thicker wire wheels used on angle grinders, still not perfect though. Grinders can move the surface of the metal over pits trapping rust underneath, which is what I think you are referring to. I have a media blast cabinet, for parts that can fit inside. I also have a spot blaster, which will clean small areas on flat metal, about the size of a 5p, by enclosing the area being blasted in a rubber shield. That really is handy. On motorcycle (spoked) wheels I can remove the tyre, blast the end of the spoke nipple, freeing it off and making it look like new. I wasn't going to suggest media blasting, because there is the danger of media getting in the engine and bearings, and it can warp panels. You can always rebuild an engine though, not so easy if the chemicals go wrong and carry on dissolving the car over the next few years underneath the nice new paint. I have never had luck with rust convertors. I would rather take my chances with a panel prepared with a wire wheel and some zinc primer over the top. (Edit: I found a piece of wire off a wire wheel in a Jensen oil pump that had sheared it's drive. Nothing is without risk it seems!)
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by Chris_R » Thu Aug 13, 2020 10:01 am

With rust converters you have to think at the molecular level which will explain Gordon's original comment "Hammerite rust treatment looks good when it turns the rust spots black but if you scrape it when dry the rust is still there !".
A rust converter can only work on the rust it comes into contact with, it does not penetrate down through the rust. So it will convert the surface rust but having done the conversion it stops converting deeper into the rust which remains below the surface. The key on this is to remove by whatever means all visible rust, including where it has pitted until you have what appears to be completely clean metal. Although to your eye it will appear to be 100% clean there may still be some rust invisible to the naked eye and that is the time to apply rust converter as the layer will be so thin and sparse the converter will convert all of what is there.
Starting with something like this:
2012-10-28-193.jpg
2012-10-28-193.jpg (106.43 KiB) Viewed 472 times

You need to get to something like this and then apply the rust converter:
2012-10-28-196.jpg
2012-10-28-196.jpg (91.03 KiB) Viewed 472 times

I have an air driven surface conditioning tool which is a mechanical rust removal method, it needs a powerful air compressor to supply enough air and it's quite slow going but doesn't create heat in the metal which can happen with using a wire wheel. That is what I used to clean the surface shown in the pictures above. I think the advantage of this particular type of mechanical removal is that the design of the tool allows the wires to get into pits in the surface instead of skimming across the top. They're loosely mounted and so they sort of chip away at the rust instead of scraping it away like a normal wire wheel does.
Rustbuster tool.jpg
Rustbuster tool.jpg (42.06 KiB) Viewed 470 times
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by Keith » Thu Aug 13, 2020 11:15 am

Chris_R wrote:I have an air driven surface conditioning tool which is a mechanical rust removal method,


These are very good plus they leave the surface "keyed" which makes the subsequent primer coat adhere much better.

If you used one of these, then phosphoric acid, then a "rust-killing" primer, before any top coats, it should hold back any further corrosion.
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