Rust Converters

[mikewilkes]

I have a steel Cat, one off built by a boatbuilder for himself 25 years ago, so dont know whether that classifies as a "Classic" but one off you experts may be able to help me on rust converters.
We have used " Kurust" (Hammerite make it I believe) in the past and it seemed to work very well. Having trouble finding the equivalent in Spain but have got some stuff which says it is basically phosforic acid - same I guess as Kurust - but it does not seem to work anywhere near as well.
After all that preamble my question is really what is the best way of treating rust other than sand blasting?
Thanks,
Mike

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[AndrewB]

Rust Treatment

Most of the converters are based on phosphoric acid, once known as 'Naval Jelly' which I've still seen on sale in Spain, and agree is not as effective as the specialist (but much more expensive) preparations. Stuff like Kurust seems more concentrated, but also contains a primer which seems to help as it allows the rust treatment to be left on for a day or two with no risk of exposing bare metal to start re-rusting. Also, a problem with fluid phosphoric acid treatments is that if you don't scrupulously remove any unconverted acid, it will later attack the paint. I used Kurust for some years but then switched to a tannic acid based preparation, Fertan, which several people here swore by. Still not convinced though that it is really that much more effective.

To be honest, I don't think any chemical treatment can be regarded as more than a temporary solution except on the thinest layer of rust, as it really only converts the surface layer of the rust leaving it to work away beneath. The rust patch will be back again within a year or so. If you can't sand-blast, which is definitely the most effective but a messy treatment requiring much preparation, then a combination of chipping followed by angle-grinding and wire-brushing¹ must be used to remove all the rust completely back to bare steel. A precautionary dab of the chemical treatment will then deal with any last remnants.

<font size=1>¹Wire-brushing means with a heavy-duty power brush. Do it too lightly and you simply 'burnish' the rust rather than remove it, no use at all.</font size=1>

 

[mikewilkes]

Re: Rust Treatment

Thanks for that Andrew

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[DogStar]

Re: Rust Treatment

I recently heard about a method of rust treatment that was quite innovative. I think they're using it on the Cutty Sark. It was developed by a guy in Portsmouth who had an old navy rust bucket. He basically rigged the hull up as a cathode, flooded it with electrolyte and dipped in a steel anode. All the rust was eventually seemingly replaced. The transformation was extraordinary. I tried to find some info on the process using google, but no luck yet.

<hr width=100% size=1>I'd rather have a bottle in front of me than a frontal lobotomy!

 

[PaulS]

Re: Rust Treatment

I have successfuly used that technique to rejuvenate old tools which had rusted badly. It works quite well. It seems to leave a coating of carbon where the rust was. I assume that's the carbon which was in the steel which rusted.

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[PaulS]

Re: Rust Treatment

BTW..to find it using Google try using the search term "electrolytic rust removal"/

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[Peterduck]

Re: Rust Treatment

I fully concur that most of the rust will have to be removed mechanically, leaving any chemical process to treat the last fine film only. For parts which can be immersed I have had success using a 10% solution of Molasses. It takes about a week of immersion, but removes even thick rust. You could do worse than paint a thick layer of neat molasses on your hull and leave it for a week. Wash it off and see what effect it has had.
Peter.

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