When I recently brought ‘Alice’ back to Greenford for some work, I was aware that one of the jobs I had to do was to repaint the inside of her tender tank. The construction was welded steel, with a removable top plate, water space surrounding the coal space, and also underneath! I did this to a) maximise water capacity b) try and keep the weight fairly evenly distributed c) to give a sloped coal space which is easier to shovel from. In practise, this all worked well, but was exceedingly difficult to paint underneath the coal space.

When I built her, I gave the inside of the tank two or three coats of white smoothrite paint to protect it. I chose white so that any rust would show up fairly quickly – which it did after about eighteen months (the tender normally has water in it – we do not tend to drain down tenders during the week).
Having had a rotten time painting the inside initially, I really couldn’t see how I could strip the old paint off by conventional means in the really awkward areas – and leaving a little bit in a vulnerable area just wasn’t on, as it would lead to serious corrosion that I couldn’t do any thing about. I then remembered reading something on a website for model engineers – Alan J Stepney (see my links page) – about how he de-rusted an awkward bit of a job that someone was working on by using electrolysis.
His technique was to mix up a solution of sugar soap in a plastic container – a table spoon for every gallon of water – dangle the job that wanted de-rusting in the solution with 12v (negative - cathode) connected, and also dangle an anode of bright steel and leave it for twenty four hours.

Why not take this principal a bit further, I thought. If I connected the whole tender to the negative, filled the tank right up with a sugar-soap solution, and then dangle an anode in, it should work, and certainly get into every crack or crevice that I certainly wouldn’t be able to by hand!

A short while later I had it all rigged up, connected it to a battery charger – and nothing happened…. No volts from the charger…. This was a new one I had bought from Halfords recently, and I’d only used it once. I checked the fuse, metered it out, got a miniscule voltage reading ….. obviously faulty. I took it back to Halfords and swapped it, hooked it up to the tender – and still nothing!
When all else fails, read the instructions. There was a little note at the bottom which said in effect that the charger wouldn’t power up until it was connected to a battery – so there was obviously some sort of sensing circuit – not very useful….
However, I got round this by simply putting another battery in parallel.

After a couple of hours a thick rusty coloured scum started developing, getting thicker and thicker, until next day there was a two inch layer of the stuff (quite revolting).

After two or three hours

don't use your Mole Grips for this...

I then drained the tank down hosed it , rinsed it and got rid of all the loose detritus to expose a thoroughly cleaned tank. No effort.

When thoroughly dry, I then gave it three coats of bituminous paint designed for the inside of water tanks (I finally got it from B&Q after a lot of searching) which should hopefully last a good long time.

In short, this is a really good way of de-rusting any steel objects - no elbow grease involved, and you know it's getting every where that matters!

Nice shiny bitumastic paint!