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After finding a lot of small off the shelf solutions were too expensive or ineffective (usually both) I read somewhere that the main ingredient was Phosphoric acid.

I found I could buy 5 Litres of 85% Phosphoric Acid for about £20 from APC Pure - a chemical company.

https://apcpure.com/product/phosphoric_acid_85_acs_fg

I have found this can be diluted at least 50% and an overnight soak removes all rust. Same as with other treatments, getting rid of the loose flaky stuff makes it work quicker.

But results have been a lot better than anything available off the shelf for a lot less cost.

Neat, it is quite thick but not like a gel - it does work ok on vertical surfaces, but best for items to soak.

And goes without saying - need to be quite careful with it. Even at 50% dilution it "cleans" concrete floors very well.

I use phosphoric acid more than any other rust removal chemical or technique. It is indeed quite effective.

I offer one bit of caution. Phosphoric acid can be particularly aggressive on high-carbon steel. If you have hardened parts that need cleaning, don't leave them unattended for too long. Check them frequently to insure critical surfaces are not damaged.

I use Gold Speed which is a 40% phosphoric acid rust killer.

Very effective stuff just keep it away from cuts on your fingers.

Tupers wrote:Very effective stuff just keep it away from cuts on your fingers.

Right you are !

I have some ugly scars on my hands from where I got acid in cuts. I only made that mistake once. Rubber or vinyl gloves are a must when working with phosphoric acid.