1kg of Deox C is about £15 plus postage, whereas 4kg of citric acid is about £14 delivered from eBay - big difference. I must admit I thought the Deox C worked better but hard to compare unless the exact same things are being de rusted. The price difference is huge so certainly worth trying the citric acid.
Also, you can pick up citric acid from local shops that sell wine making stuff I believe.
I bought a 10kg bag from ebay for £25, there are lots of sellers and its all the same stuff. I mix up about 1/2 to 1 kg to a bucket of hot water, then keep it hot with a cup boiler.
Here is an example, you will need to strip any grease or paint off first to get a result like this. Given my jag is very rusty I have to use it a lot.
From memory about a day or so, for best/quickest results, its best to take them out every 4 hours or so and give them a scrub with a wire brush to remove any flaking bits to let the acid in to do its work.
£7.99 for 2KG. I reckon I've used about 400 grams so far, maybe a little less. The great thing about using the wallpaper paste is that you can control just how thick you want the gel to be. Because the wallpaper paste is an adhesive I find it to be better when it comes to vertical surfaces as opposed to to the Deox Gel, it clings to the surface more so.
Well, there isn't any instructions with the citric acid and as for the wallpaper paste I don't think they figured it'd be used in recipe for rust removal
Firstly, mix up the paste with water, de-ionised water would probably be the best considering it's purity. I used tap water though and I've not had any issues. Bear in mind that consistency of the paste you're making should be very sticky and dense because as soon as the citric acid is added it'll really thin out.
You don't need a lot of citric acid, 150-200 grams will suffice for a finished solution of 500 ml. Once applied, the usual cling film, tape it down and wait 24 hours. Scrape off, flapper and/or wire wheel, second or third application depending on how much visible corrosion has gone. I do believe it works as well as Deox Gel since when I came to phosphate the surface afterwards, hardly any dark areas appeared in the pits or pores.
The solution when made up will be far clearer in it's colour, when it attacks the corrosion it will darken but shades and colours differ to the Deox Gel when it's working but the result is the same.
Also put o=some washing up liquid in the mix it helps break up any oil on the surface of the metal.
I will be trying the gel method next week, I have always used it as a soak in the past.