How to Remove Rust With Ospho

Updated February 21, 2017

Ospho is a chemical compound that can be used to treat objects that have begun to rust. Ospho removes rust by altering its molecular structure and transforming it into iron phosphate--a hard, black substance. Not only does Ospho dispose of the rust, the previous oxidation is transformed into a rust-resistant material. Because the substance that Ospho leaves behind may be unattractive to some individuals, it is commonly used to get rid of rust on objects prior to painting them.

Scrub the rust with a wire brush or scouring pad to remove excess oxidation before applying Ospho. Wipe the object clean with a damp cloth.

Check the temperature. If you are working outdoors, it is recommended that the temperature be above 2.22 degrees Cor Ospho to work properly.

Apply one coat of Ospho with a damp cloth. If the object you are applying the Ospho to is particularly large, you may opt to use a paintbrush for the application.

Allow the Ospho to dry overnight. Once the Ospho is dry, it will leave behind iron phosphate in addition to a loose, white powder.

Check to make sure that all of the rust has been transformed into iron phosphate. If the object was particularly rusty, small patches of rust may remain. In this case, you may wish to apply a second coat of Ospho.

Brush off the white powder with a dry cloth or paintbrush.

Paint the object, if you so desire.


If you are concerned about the appearance of the iron phosphate, test Ospho on a small, inconspicuous area before applying the substance to the entire object. For a particularly smooth finish, you may apply one coat of Ospho, allow it to dry for 30 minutes, wash it away and buff the remaining surface with a soft cloth. This process may need to be repeated several times to be effective.


Ospho contains phosphoric acid, which is dangerous to children and pets. It should be kept tightly sealed and out of reach of children and pets at all times.

Things You'll Need

  • Wire brush or scouring pad
  • Clean cloth
  • Ospho
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About the Author

Ciele Edwards holds a Bachelor of Arts in English and has been a consumer advocate and credit specialist for more than 10 years. She currently works in the real-estate industry as a consumer credit and debt specialist. Edwards has experience working with collections, liens, judgments, bankruptcies, loans and credit law.