Productivity Factors for Painting Steel

Cleaning

Making sure that the surface is free of all accumulated dust, grime and dirt prevents peeling and improves the paint job's overall finish. Pretreating all rusty areas with rust converter improves the surface's ability to stick with the paint, even before washing and sanding. Surface contaminations, wax, and grease can be removed easily using dishwashing soap, trisodium phosphate and degreasing solvents such as denatured or 90 percent isopropyl alcohol, acetone and methyl ethyl ketone.

Because imperfections in metal -- such as dents and scratches -- get highlighted after painting, sanding is a step that simply cannot be skipped. Experts recommend using a sanding block for a more uniform end result. The goal in this step is a dull, hazy, or milky finish. When dealing with an already-painted surface, the color of the new coat should be considered. If it closely resembles the original, the surface need not be sanded down to the bare metal. After sanding, the surface goes through another round of washing or wiping with dishwashing soap or solvent.

Primers play two roles in paint jobs on steel: adhesion enhancement and rust inhibition. A thin layer of oil-based rust inhibitive primer has components like zinc chromate that sacrifice themselves to corrosive agents, thus protecting the metal. For best results, two types of primers should be used. First, a very thin and smooth layer of an etch primer that chemically adheres to the substrate, and second, two to three thin coats of a regular primer that provides mechanical adhesion via the small sanded scratches. Once the sprayed-on coats of primer have thoroughly dried, a round of wet sanding and cleaning follows.

The best paints for steel contain rust-inhibitive pigments that can extend the life of the metal, such as barium metaborate. Two to three coats should do the job of hiding old paint and the primer well enough, though experts recommend an additional coat after hiding. They must be allowed to dry properly between coats. For steel, airless sprayers provide the best finish compared to brushes and rollers, and have the added advantages of better consistency and greater convenience.