OSPHO is a rust inhibiting coating that provides a sound base for subsequent primers and paints.
When applied to rusted surfaces, OSPHO causes rust (iron oxide) to chemically change to iron phosphate - an inert, hard, black substance. Where rusted metal is exceedingly heavy, two coats of OSPHO may be necessary.
The OSPHO dries to a tough, hard, rust-resistant - surface ready for priming and painting. A paint job will last longer after an application of OSPHO because paint coating securely attaches to the surface, so corrosion-producing moisture and oxygen cannot gain access to the metal. And subsequent paint coating securely adheres better.

You do not have to remove tight rust. Merely remove loose paint and rust scale, dirt, oil, grease and other accumulation with a wire brush. Then apply a coat of OSPHO as it comes in the container - let dry overnight. In harsh conditions, best results will be obtained if you apply a primer over the OSPHO, then paint.

• An etching cleaner/rpimer - not a paint
• Water-thin — goes on easily, covers a larger area than paint
• Suitable for exterior and interior applications
• Balanced formula of phosphoric acid, dichromate, wetting agents and extenders
• Typical coverage is 600 sq ft/gallon
• Works best when overcoated with oil-based primers and paints
• Test before using under epoxy or latex-based paints
• Can dissilve bleeding rust from many previously painted surfaces; test a small area first to check for dulling or peeling