Getting rust off metal is a project that has plenty of options and plenty of products requiring your money. Corrosion is caused by an electrochemical reaction when metal combines with oxygen and water to form black, brown or red rust. Depending on the accessibility and location of the rusted metal, you may want to combine or at least consider several options.
The best method by far for treating rust on metal is sandblasting. It is one of the easiest ways to get the job done and leaves the surface completely rust free and ready for painting or other procedures. It will require thorough cleaning of the metal and the entire area around the project afterward since it is a messy procedure.
This is not the best procedure for nook-and-cranny work, however, since the sandblaster cannot get into tight corners and out-of-the-way places.
Simple household products like a tablespoon of lye or a tablespoon of Arm & Hammer Washing Soda per 1 gallon of water work just as well as more expensive cleaners.
The process requires the metal or metal part to be immersed in a water solution, which can be difficult for bigger items.
Less Caustic Acids
Less caustic types of acid, such as Ecotec, can work well. Ecotec removes tarnish and rust from metal and steel without harming the underlying metal.
Soak the rusted part from 15 minutes to several hours (depending on how much rust is present) and then wipe off the rust. Ecotec can be heated to speed up the removal process. After the rust is removed, rinse with water and dry. Finish with a rust preventative.
Ecotec may be more costly than more caustic acids, but is easier to dispose of when finished. It is biodegrable, non-toxic and environmentally benign.
Naval Jelly helps when a gel is needed to cling to a surface. The concentrate DuPont 5717S works well, but can be difficult to work with for some projects. Other plain phosphoric treatments include Rust-Mort, MP-7 and Mirachem 250.
There are also phosphoric acid treatments with zinc, such as DuPont 5718S and Metal-Ready. The zinc residue on the treated surface is intended to protect the metal from more corrosion. The zinc does not make much of a difference and is not the worth the extra money.
Products such as sulfamic acid and hydrogen chloride eat into metal at a faster rate than rust, meaning that while the products attack the rusty surface, they can also cause as much harm as they do good. Acids in this category include CLR - Calcium, Lime & Rust Remover and Envirosolve 1000.
Conversion coatings, available at hardware stores, go on and stay on metal. The coatings, such as Extend, One-Step and Rust-X, claim to convert underlying rust to an inert substance and leave a black primer for future work.
With their quick drying times, it is tough to believe the conversion coatings make much of a difference on metal projects.
Useful Tools, Other Treatments
A wire brush is a great tool for any project involving rusty metal. Brushing the metal before and after any of the above treatments is a good way to get all the rust off.
To stop car rust, consider Eastwood's Heavy Duty Anti Rust. The wax film sticks to bare metal, as well as painted surfaces.
A good all-around-treatment is Rust-Oleum, able to stop rust on many projects around the home.