Molasses for Rust Removal - the suck it and see experience

Why suck it and see you ask? Simply put if trying the molasses method for rust removal is effective and I’m happy with the practical result then I don’t feel the need to spend endless hours researching the chemistry for why it works. That leaves me endless hours for looking at cycles and cycle parts on the Internet.

The good news for the reader is that no research means no big words such as ferrous, oxidation and anabolic reaction. This is a simple discourse relating my experiment with molasses for the removal of rust and the results in plain lingo.

Like most of us in the hobby of conserving old cycles I was interested in finding a practical alternative to sand blasting to remove rust so that chrome, nickel (if you’re lucky) or paint and transfers are not damaged while cleaning the cycle frame and components of rust.

Aluminium foil rubbed on a chrome surface with water as a lubricant works well on light rust as does 0000 steel wool using as a lubricant. I have used 0000 steel wool on painted surfaces as well with good results. The problem with 0000 steel wool is the residue which hinders the application of paint or conservation wax.

Commercial rust converters, based on oxalic acid, can achieve good results in converting the rust but they don’t remove the rust, instead behind leaving a grainy surface of black residue in place of the grainy surface of brown residue you had before treatment. At least they stop the progress of rust if the surface is protected after treatment.

There is an abundance of anecdotal evidence that a molasses and water mixture is effective for rust removal. I had my doubts until having dinner with an engineer who told me he had used a molasses bath to remove rust from vintage cast iron lathe components. He was so impressed with the result that he considered experimenting with and marketing the most effective molasses solution. This was the kick I needed to give it a go.

Molasses to water mixture ratio: My bath is a mixture of 3 parts water to 1 part molasses in a cut down 20 litre plastic container. I have heard of ratios of 5 to 1 and 10 to 1 being used successfully. With molasses available from stock feed suppliers at around $3.00 per litre I decided 3 to 1 was still cost effective to make a 15 litre bath in which fairly large parts could be submerged. 

Parts need to be clean of oil and grease before treatment so the liquid can come in direct contact with rust. I have found that there is no need for cleaning off rust scale as the mixture will dissolve it. The more rust the longer it needs to stay in the bath. Light to moderate rust seems to be removed in about 2 weeks. I have left parts in for longer that 2 weeks with no noticeable deterioration of the base metal or any chrome or paint coatings as long as the coatings are well adhered to the metal below.

CAUTION: I haven’t treated parts with water slide transfers so don’t know the result.

The engineer I mentioned earlier had a college that used a 44 gallon drum as the mixture container. It was an upside half and the molasses mixture ate away the aluminium bung in about 3 days. ALUMINIUM PARTS CANNOT BE TREATED IN A MOLASSES BATH!

Once removed from the bath the parts are simply washed off with water. The results are very pleasing with all rust removed from surfaces including hard to get at nooks and crannies. The metal surface is left a light grey and can vary from smooth to looking like it has been sand blasted depending on how deep the rust was. As the part dries it immediately starts to get a slight orange tarnish as the rusting process starts again. I usually apply Ranex rust converter at this stage which converts the tarnish and stops the rusting process leaving a surface ready for conserving or repainting.

If I am conserving a piece and wish to retain the original patina I apply a conservation wax. The wax does a great job of bringing original colour and detail to the fore again. Parts that I treated with molasses, Ranex and then conservation wax up to six months ago have not started to corrode again. The July – August 2013 edition of the Spoke n Word contains and article on wax and where to source it.

Other discoveries: My molasses bath grew mould for a period of time early in its life then the mould disappeared and hasn’t come back again.  I wondered how long the molasses mixture would remain active and a friend said he had a brew that has been going for a number of years requiring an occasional top up of water to allow for  evaporation. The mixture has quite a strong beer hops smell so you wont get away with hiding it in the house.

Hope this helps making your cycle restoration easier.

Glenn Huffer