Painting exterior metal objects presents particular problems because of the composition of the material and constant exposure to the elements. Metals can deteriorate rapidly because of moisture from rain and snowfall, as well as salt spray, acid rain, smog and other environmental factors. Outdoor fixtures such as steel poles require a durable finish that can stand up to these destructive elements.
Metal Painting Basics
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Moisture is the enemy of all metals, particularly in outdoor environments. Small imperfections in finishes can allow the intrusion of water that begins to break the chemical bonds that hold metal together. The stronger and more thorough the coating on the metal surface, the better able it is to withstand these chemical reactions with moisture, and the longer the finish will keep its good appearance, as well as keeping the structural integrity of the metal itself.
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Surface Preparation
Steel poles that are exposed to the elements often have pitting and surface rusting that signal the beginning of a corrosion problem. You must first remove all surface rusting from the poles before attempting to put a new finish on the steel or the corrosion will continue to react with the metal beneath the new paint. Removing rust generally requires sanding, either by hand or with an electric sanding tool, or by treating the metal chemically with a phosphoric acid product.
Metal Primers
The best method of painting exterior steel surfaces is the two-coat system using a primer as the first coat and an acrylic latex paint for the top coat. High-quality metal primers contain rust-inhibitors that will help to prevent corrosion. These primers must be applied as a base coat and allowed to dry completely before applying the top-coat paint. Only use a primer specifically formulated for metal.
Rust-Inhibiting Paints
To give the steel poles the best protection against corrosion possible, use a rust-inhibiting paint formulated to resist metal corrosion. These paints are available in a wide variety of colors and textures for every purpose. Follow label directions for application and allow to dry thoroughly.
Direct-To-Metal Paints
A newer option for painting exterior steel items is direct-to-metal paint. These paints combine a primer with a top coat for convenient application. Though these generally do a good job, they do not provide the rust protection of the standard two-coat application method, according to the PaintPro website.
Other Paint Methods
Steel poles located in particularly harsh environmental conditions might need frequent painting. In this case, homeowners might consider having a powder coat surface applied to the poles. Powder coating uses paint pigment applied electrostatically with a resin bond, according to the Powder Coating Institute website. The coating is then baked on at high temperatures for a tough, high-quality coating that resists weathering and corrosion. Powder coating is generally used when an attractive surface is desired for the steel material.