Removing Rust

The author’s ‘test lab’ setup for testing various products for their effectiveness in removing rust.

Words and photos: Richard Vaughan

Rust is an ever present concern for most woodworkers because so many of the tools we use are prone to it. It prevents true sharpness, clogs adjustment and marks wood. It’s easy to prevent, and that’s another story, but getting rid of it is far simpler than many realise, and there are quite a few ways of dealing with this old problem, including a range of dedicated products.

A vinegar bath derusting some of the many tools for the Rambutso project.

Simple, effective and cheap was definitely in mind when I needed to restore a lot of donated but neglected tools before
shipping them for community projects in Rambutso, Papua New Guinea in January 2016 (see AWR# 91), and later again in January 2017 when over half a tonne of tools were restored and shipped.

It’s unlikely you’ll have to deal with such a quantity, but the methods available are worth sharing for whatever your needs may be, such as inherited tools or luck at a second hand market.

Scrub up

With just about any approach you’ll need to first remove surface dirt and any grease or oil residue to get effective penetration of whatever rust remover you use, and the simplest way is a good scrub with soapy water. Along with kerosene and turps, there is a range of effective degreasing products available should heavy oil or grease be a problem.

On the surface

Some people have ‘rusty’ or ‘acid hands’ because their natural body chemistry will immediately leave prints on any steel they handle. The light rust spots that can form from sweat can be removed with scouring pad, sandpaper (at least 320 grit for minimal surface damage) or steel wool. Awareness and prevention are the best way to deal with this.

Citric acid

I used this for my story on restoring a plane in AWR#57. Citric acid helps put the fizz in bubble bath bombs as well as being a staple in food preparation, so it is readily available from supermarkets and sources online. Fill a plastic storage bin with solution to make a bath to suit the tool. A couple of tablespoons per litre of warm water is a good start. Soak overnight or longer if needed.

Oxalic acid

This is the strongest of the organic acids and derived from such familiar plants as rhubarb, spinach and tea leaves. It’s a less- nasty-to-people kind of acid than the commercially used hydrochloric and sulphuric acids which will attack metal once they have destroyed the rust. The fumes as well as the acids themselves are unnecessarily risky and not suited to our purpose.

Oxalic acid is sold under a variety of names at hardware shops for rust and stain removal. It is also good for removing superficial iron stains from wood so I keep it handy. Be warned though: it is organic but you are handling a concentrated form so you do need to protect yourself well from breathing any dust should you wire brush or sand it when dry.

Citric acid is preferable to oxalic acid because the iron salts formed are more soluble. Oxalic acid can leave a green deposit on steel. Citric acid forms iron citrate in solution which becomes colourless in direct sunlight.

Phosphoric acid

Phosphoric acid is the basis of rust converter products as it reacts to leave a protective coat over the metal, but it does not necessarily prevent the rust beneath from continuing its damage, so although it suits some applications I’m not keen on it.

How slowly molasses works can be seen here after three days soaking. It’s hard to distinguish between the treated and untreated.

Molasses

This is another readily available substance used to make a bath for soaking rusty steel and iron. It is in fact the citric acid in it that does the job. Between 1:5 and 1:10 in water works fine. More dilute will be cheaper but slower. Molasses is priced okay in supermarkets but cheaper in volume from horse feed suppliers. Slower acting than most treatments, it does have the appeal of being mild to handle and not a concern when it’s time to dispose of it.

Good old vinegar with a spoon full of salt had destroyed the rust on this square blade in 24 hours. As with the citric acid I didn’t check it along the way, just gave them this proven time, though they may well have done the job sooner.

Vinegar

Generic white vinegar is cheap and very effective. Adding salt will increase the acidity. Several tablespoons up to a cup of salt for five litres of vinegar is a good mix. For serious rust you may need to leave the tools to soak for a couple of days, although 24 hours usually sorted all the ones I’ve had to deal with.

After the acid bath

After scrubbing with scouring pad and/or wire brush and then a good rinsing in fresh water you’ll need
to neutralise any acid remaining. Soak the tools in a solution of baking (also called bicarbonate of) soda. Use several tablespoons to five litres of water, for about 10 minutes. It’s readily available from supermarkets.

Electrolysis

Those inclined may fancy a battery charger and a container full of water with washing soda (sodium carbonate) or baking soda (sodium bicarbonate) solution to enhance conduction. Be aware that washing soda is strongly caustic. A teaspoon to five litres of water of either is sufficient. Using sodium chloride instead gives off dangerous fumes so best not try it.

You attach the positive terminal to a sacrificial bit of steel with plenty of surface area such as an old steel (not aluminium) baking tray or old stainless steel pot lid, and the negative to the steel you want to de-rust. Remember: NO = Negative to Object. Please note that this is an overview of methods and you will need to do further research
to attempt electrolysis safely and effectively.

Dedicated products

 

Rusted Solutons Rust Remover is an Australian formulation which comes as a liquid to be mixed 1:4 with water, and as a gel for when submersion in a bath is not feasible. Both are re-usable until obviously dirty. A one litre bottle for $65 mixes up to five litres bringing the cost down to $13 per re-usable litre.

Rust Remover liquid certainly lived up to its name with this result after four hours. Evapo Rust gave a similar result.

The gel really does need to be 4–5mm thick as instructed. It is ineffectual when the coat is thin. But there certainly are cases such as on machinery, when dipping wouldn’t be feasible and gel would work.

Evapo-Rust has an impressive list of what it doesn’t harm, including skin, rubber, plastic, copper, PVC brass and vinyl. Thirty minutes to remove rust is announced on the bottle but several hours is more realistic. It gives anti-rusting protection for a week or two after de-rusting so post treatment flash rusting is not an issue. One litre for $37 from Supercheap Auto doesn’t sound cheap, but the liquid can be repeatedly re-used.

After five hours soaking in Rust Off the phosphoric acid had converted most of the rust but it couldn’t get behind the material jammed in some teeth.

Rust Off is a phosphoric acid solution so it converts the rust to a coating rather than lifts it. It’s convenient and fine for uncomplicated surfaces like rust spots on the car, but will be a barrier against the subsequent rust prevention I recommend for woodworking tools.

Before you start

The cutting edges of chisels, gouges, spokeshaves and planes can be rendered ineffective by rust pitting, so before you attempt to restore a market bargain do consider whether you will be left with clean steel that can give an unpitted edge, or at least can be ground back to be pit free.

Please be aware that these methods are for steel and iron. Other materials such as copper and zinc and plastics may be harmed by some of these treatments. Evapo-Rust and Rust Remover claim to not harm such materials.

Another thing to be aware of is the possibility of metal embrittlement. It’s a process I won’t attempt to explain but I do know that you don’t want springs to be affected by it, so don’t put spring metal in acid treatment or electrolysis. Evapo-Rust and Rust Remover claim no harm to the metal under the rust and so seem to be safe and easier de-rusting options than sandpaper or scourers.

Not the end

After the modest testing for this article my conclusion is that soaking rusty tools in vinegar or citric acid is a cheap, convenient, safe and effective method of rust removal with the proviso that you need to neutralise the acid, and should not use it for spring steel.

Both Rust Remover and Evapo-Rust are effective with the advantage of not damaging associated materials or the steel beneath.
No matter which method is used, once the metal is rust free and the treatment neutralised, you will need to take preventative measures against the rust returning. It never sleeps.

Rusted Solutions Rust Remover supplied for review from www.rustedsolutions.com.au
Evapo-Rust is available from Super Cheap Autos.
Rust-Off can be obtained from Bunnings.

Richard Vaughan is a furniture designer/maker in Brisbane who also runs woodwork classes. See richardvaughan.com.au