Thought I would add today some detail about how I am treating the rust. Might be of interest to some?
My pvc pipe with vinegar and citric acid was going to cost too much to make in a big quantity. So this time just using a stronger citric acid solution. I picked up a 25 kg/55 lb bag of it from a farm supply place.
http://www.eem.com.au/ They use it a lot in wine making to clean out the stainless steel tanks after using caustic soda. Can also get it from pool supply places, or where you might buy ingredients to make bath bombs etc.
It just looks like sugar. Can get it in two forms, anhydrous or monohydrate. Either works the same so get what ever is the cheapest. I used anhydrous and got a 25 kg bulk bag for the same price as 5 kg ones sold else where!
I used half a bag to make up just over a 5% solution in a bath tub that was given to me. The bath held 225 litres/59 US gallons to which I added 12.5 kg/27.5 lb of citric acid. I found the volume of 1 kg of the acid took the same amount of space in the bucket as 1 litre of water that was marked up the side.
I had carried buckets of hot water to the shed to help dissolve the citric acid. I counted the buckets as well so I knew how much water it held. I added a bit of acid at a time and stirred it until it dissolved.
The bath is not deep enough for the whole wall to be done at once. I have coated the wall above the water line with lanolin to stop it rusting while the rest gets done. You can dip your bare hands into this ratio if you have not cuts etc. Can tingle a bit, but washing with soap stops it. Gloves are a better idea.
Just to show how well this works, I just threw in a pair of Willys headlight buckets also.
These have not been touched at all with any treatment before going in.
Took this shot after 2 days and they have not been disturbed at all. The rust is just falling off!
Day three doesn't look that much different so decided to pull them out and see if it was long enough. The more acid you use, the quicker it will go.
This is what the inside looked like just before scrubbing started.
Just used a nylon washing up brush.
All the rust is just washing off.
It wont remove paint unless it is flaky or not well laid down in the first place. I found some areas with over spray on other parts, just washed off. It does soften the paint though and a bit of scrapping usually gets most off
I use a stainless steel scourer for a bit better job.
To neutralise the acid I just added a couple of tablespoons of bi-carb soda to some hot water. Same as baking soda but not baking powder. This step is especially important where any acid could be trapped and not easy washed away with water.
Need to dry it as quickly as possible to stop flash rust. Use an air gun or propane torch etc to dry it. Then it must be coated straight away in primer or some thing else. I use lanolin myself as wont be painting for some years yet.
Quite a difference from what I started with 3 days earlier.
The left one I ran the wire wheel over as well so why a bit brighter than the other.
The wall was turned over after washing off the acid. Also the lanolin was removed with thinners so it doesn't stop the acid from working on the non dipped part. Lanolin was rubbed on the part that has already been done.