To avoid problems, proper steps must be taken in preparation and application of Fairhill Industries zinc-rich rust repair coatings. Temperature, mixing, spray atomization, contamination, zinc salts, over spray and dry spray, types of topcoats, and topcoat application must all be considered.
The surface must be cleaned so metal-to-metal contact can occur between the zinc from the coating and the steel surfaces. Fairhill Industries zinc rich coatings will not provide the galvanic protection for which they were designed if applied over rust, old paint, or anything that will prevent the zinc pigment from contacting the bare steel. A common application is weld touch-up. The overlap onto the existing coating should be minimized as the overlap is a potential failure area. Extra care should be taken in preparing and coating the overlapped area.
Fairhill Industries “Prime Zinc” should be applied by either conventional or airless spray equipment with agitated spray pots. Because of the heavy pigment weight of these materials, hose lengths should be kept as short as possible.
Brush application should be done for touch-up, care must be taken to stir the paint adequately to keep the heavy zinc pigment from settling.
IMPORTANCE OF SURFACE PREPARATION
The quality of the life of Fairhill Industries coatings depend on some degree on the quality of surface preparation. Therefore, this should receive thorough consideration. The primary functions of surface preparation are to clean the surface of material that may induce premature failure of coating and to provide a surface that can be easily wetted for good coating adhesion.
Typical contaminants that should be removed during surface preparation are moisture, oil, grease, chloride salts, sulfate salts, rust, corrosion products and dirt. Tightly adhered or intact mill scale does not have to be removed for mild atmospheric exposure. However, if the steel surface is to be exposed to severe environments, such as chemical exposures and immersion in fresh or salt water, then removal of mill scale by blast cleaning to a minimum SSPC-SP10, “near white blast” cleaning is necessary.
Ideal surface temperature for application is 60° to 90° F. If the surface is too hot, the solvent in the topcoat may evaporate before good adhesion is achieved. If the surface is too cold, solvent or water evaporation may be retarded. All ambient conditions should be considered.
Prime Zinc coatings are formulated to be applied at a dry film thickness from 1.5 to 3 mils at greater thickness, mud cracking and loss of adhesion can occur.