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Old 06-05-2018, 09:05   #1
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Correct/best rust converter

Hello:
I am currently in the process of replacing the wooden rub rail bolted to the side of my steel hull. After 15 years, I tired of spot fixing rust which appeared behind the rub rail, so it all was removed and I am rebuilding the contact surface.

In the past I have used a product which contained hydrochloric acid to convert the rust. It turned the rust black, but necessitated flushing with water before applying any sealing coat. I am told to stop the acid from continuing to work.

During my recent trip to the local chandler, I purchased the recommended converter that turned out to be phosphoric based.It turns the rust mid brown and leaves a chalky residue on the surface which can be scratched off with a finger nail. I was also told not to flush the surface as with hydrochloric acid.

Due to colour differences, Iím not sure the phosphoric has done what is expected. Plus Iím inclined to take a green scrubby to the phosphoric surface before starting the epoxy layers, to provide a solid surface.

Can any one suggest what is the correct/best rust converter to use?
Will applying hydrochloric acid onto the phosphoric converted rust provide any benefit at this stage? I appreciate any views.

Thanks
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Old 06-05-2018, 09:51   #2
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Re: Correct/best rust converter

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Old 06-05-2018, 10:13   #3
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Correct/best rust converter

Actually I want to think all rust converters are osphoric acid based.
Check spelling Iím sure itís incorrect.
What Iím led to believe is they convert iron oxide to iron phosphate I think and that is why itís effective in stopping rust.

However there are rust removers, like naval jelly, that is a powerful acid meant to remove the iron oxide, but if you want to use a rust converter, then you want to leave a layer of iron oxide, you donít want clean steel.

In my experience, the rust converters are more effective long term than the rust removers. However maybe if careful steps to properly treat, prime and paint maybe getting to clean steel is better. My use is mostly for things like engine blocks etc where fully stripping and starting over isnít likely.

I did a little Googling, there are other ways apparently to ďconvertĒ the iron oxide layer, but they all seem to use some form of acid, tannic acid is another one.
This link seems genuine.

All the good converters I have used did turn rust black, very black. I have used one that turned it a greenish color, and it was not that effective.
https://www.jcer.info/best-rust-converters/
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Old 06-05-2018, 12:30   #4
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Re: Correct/best rust converter

Actually rust *removers* are usually phosphoric acid, which is also why CocaCola syrup does such a good job of it. (Lots of phosphoric acid in it.) I don't recall what the real "converters" have in them, but the most effective ones actually convert the rust into a black material which IIRC is similar to magnetite, a very stable form of iron mineral ore. I've used Loctite Extend "rust neutralizer" for this, and the ingredients are mainly trade secrets. You can take a look at

https://www.whatsinproducts.com/file...eutralizer.pdf

but aside from an unspecified polymer and a slight amount of an unnamed organic acid, it doesn't say much. Like most Loctite products, if you follow directions it works pretty well. There are others on the market, usually they look like white school glue when you brush them on, and turn the rust into a black hard crust as they cure.
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Old 06-05-2018, 12:58   #5
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Re: Correct/best rust converter

I am curious to see what others come up with too.. I have used Ospho and Naval Jelly and then rust inhibiting primer too.
I am curious about this stuff, but haven't tried it:
https://www.amazon.com/dp/B001CRETZW..._t2_B000C02CDG
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Old 06-05-2018, 14:47   #6
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Re: Correct/best rust converter

Well worth buying -

https://www.amazon.co.uk/Metal-boat-.../dp/B0070QRME4


Best of all is shot blasting to SA 2.5 then lots epoxy paint, but so often just not possible and there is no magic bullet..

So after many years best I've come across is as outlined in the metal boat maintenance book. Chip, grind, needle gun to get the steel as clean as possible then soak in phos acid, leave for a while then wash and wire brush and more acid. The acid dissolves some surface rust but also converts the more tenacious rust to blackish iron phosphate ( I think) . Then wash again, and again, sanding discs on a grinder or something to get as close as poss to clean metal and get rid of the bulk of iron phosphate then wash again. Then I use a blowtorch soon after the last wash to get the steel completely dry then straight on with your epoxy of choice. Some are tolerant of less then perfect preparation. Then maybe 8 coats and hope for the best....
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Old 06-05-2018, 16:22   #7
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Re: Correct/best rust converter

Give a try to Brunox Epoxy.
http://www.brunox.com/website/produc...-Spray-en.html
It is a converter and epoxy primer at the same time. I haven't used it yet, but a couple of friends had use it with satisfaction.
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Old 06-05-2018, 17:21   #8
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Re: Correct/best rust converter

Most of the above remedies just wall off the rust. The others are acids.
The best rust remover I've found is Archoil AR5100. It's organic, biodegradable and actually dissolves the rust leaving clean metal. It's from a company that specializes in products using nano technology. Archoil has other products for oil and fuel I use. If interested archoil.com
Rusted metal I have treated contains no rust and is clean down to base metal. It comes as a concentrate and mixes with water up to 16:1. I've only used the most diluted mix. I resurrected badly rusted pliers found in the bilge salt water. Soaked overnight, it removed all the rust and the pliers operated smoothly.
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Old 06-05-2018, 19:54   #9
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Re: Correct/best rust converter

Tx for Archoil link, must try this stuff.
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Old 07-05-2018, 00:05   #10
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Re: Correct/best rust converter

Quote:
Originally Posted by Lepke View Post
Most of the above remedies just wall off the rust. The others are acids.
The best rust remover I've found is Archoil AR5100. It's organic, biodegradable and actually dissolves the rust leaving clean metal. It's from a company that specializes in products using nano technology. Archoil has other products for oil and fuel I use. If interested archoil.com
Rusted metal I have treated contains no rust and is clean down to base metal. It comes as a concentrate and mixes with water up to 16:1. I've only used the most diluted mix. I resurrected badly rusted pliers found in the bilge salt water. Soaked overnight, it removed all the rust and the pliers operated smoothly.
Not convinced I'm afraid..

I've spent a long time getting steel shiny clean and would put money on all the rust being gone.. Then on a really hot day apply phosphoric acid - fizzes and pops as the acid reacts with the rust still deep down in the microscopic pores in the steel, ain't no magic bullet...

Unfortunately the only way to test is prepare identical sections of steel with the various wonder cures, leave the sections in identical conditions and come back in 8 or so years, otherwise observer bias takes over.
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