Waxoyl is a rustproofing fluid used to prolong the life of steel car chassis and bodywork. It works by excluding water and air from bare metal and by slowing the progress of existing surface rust using phosphoric acid rust inhibitors. The fluid is a suspension of waxy particles in white spirit, which evaporates after application.
Waxoyl was developed in the United Kingdom in 1972 by Allen Forster, founder of the Hammerite paint company. It is now distributed in the United States and Europe.
Unlike the more common products which are asphalt/tar like, Waxoyl must be applied in warm ambient temperatures or heated in application, or alternatively thinned with white spirit in order to reduce its viscosity. Heating is usually done by placing its metal container in a bucket of hot water. The color of the product/solution varies. Waxoyl possesses a gold/amber tone (though black is also available) in solution, and after it is thinned by heating it is sprayable. It can be applied by brush without thinning or heating. It is also available in aerosol cans.
Waxoyl underseal is bitumen-based to resist damage in high impact underbody areas and contains the same anti-rust formulation. It is also designed to remain viscous for extended periods.