This specification covers a two-component basic zinc chromate-vinyl butyral wash primer for structural steel surfaces prior to painting.
It is intended that this coating be used primarily on clean steel free of rust and scale or on clean galvanized metal cleaned according to SSPC-SP 1, "Solvent Cleaning"; but it may be used, when specified, on steel with very slight amounts of rust. It is to be applied by brush or spray in accordance with SSPC-PA 1, "Shop, Field, and Maintenance Painting of Steel."
Basic zinc chromate-vinyl butyral wash primer is a pretreatment for metals which reacts with the metal and at the same time forms a protective vinyl film which contains an inhibitive pigment to help prevent rusting. This coating is supplied as two components which are mixed together just prior to use. The base contains an alcohol solution of polyvinyl butyral resin pigmented with basic zinc chromate. The diluent contains an alcohol solution of phosphoric acid which reacts with the vinyl resin, the pigment, and the steel. Details of the composition are given in Federal Specification DoD-P-15328.
This primer contains approximately 10% by volume of nonvolatile film-forming solids (pigment and binder). The theoretical spreading rate for a 0.5 mil (13 micrometers) dry film thickness is 320 square feet/U.S. gallon (7.9 square meters/liter). Actual spreading rates can be significantly lower.
