Q–My painted steel patio furniture is beginning to rust. The rust is light in some areas, but some places, near the welds, are heavily corroded. What is the best way to paint this and protect the steel? What about primers?
A–You are about to contribute part of the $2 billion that is spent each year in the U.S.A. on protective coatings that inhibit corrosion. Don’t worry about that figure. You probably will spend less than $25 to give that patio furniture a strong defense against the air and water that are causing your rust problems.
Many people don’t realize that the steel used in car parts, porch railings, patio furniture and other objects is very unstable. Processed iron or steel is constantly trying to change back to its original state–iron ore. You see, iron ore is simply wet, oxidized (rusty) iron. If you were to pick up a piece of iron ore at a mining site, you would have a clump of rust in your hands.
For you to slow this natural rusting process, you need to coat the processed steel with special paints that contain rust inhibitive pigments. These ingredients chemically alter the conditions at the surface of the metal, making it very hard for the steel to rust. Paints that contain zinc or zinc chromate do a fantastic job of protecting steel from the corrosive effects of air and water.
Red lead also is a super rust-inhibiting ingredient. However, lead poses a significant health risk. It is tough to find paints that contain lead. You may be able to find a commercial or industrial paint store that still carries a paint containing lead, but be careful where and how you use it. It can poison you and/or your children.
The key to successfully repainting your patio furniture lies in surface preparation, the correct primer, and a high-quality top coat. Inadequate surface preparation (cleaning, sanding, etc.) is responsible for nearly 80 percent of all premature paint coating failures on steel. By spending several more hours preparing your furniture before painting, you may get several more years of protection.
Believe it or not, you don’t have to remove every speck of rust to obtain superior results. But you do need to remove any loose rust, oils, dirt, grease and dust that would normally come off with a thorough washing, scraping and/or wire brushing. Paints are simply complex colored glues. If the paint can stick well to the substrate, even slightly rusty steel, you will be all right.
Oil-based or alkyd primers that contain high quantities of rust inhibitive pigments tend to work the best when priming rusty steel. They have a much better tendency to wet the surface and flow into microscopic cavities in the steel. (This is how the paint sticks to the metal.) In addition, these special primers are formulated not to breathe, so water vapor can’t pass through to get to the steel.
As soon as the primer is dry, you need to paint the furniture with your finish coat of paint. There are both water-based and oil-based paints that will work well for this purpose. Be sure to use paints and primers that are compatible. Most manufacturers will tell you which primer to use for a particular finish coat or vice versa.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352. Questions will be answered only in the column.
For a list of manufacturers of rust inhibitive paints and primers, paint compatibility charts, and other tips on painting steel objects, send $2 and your name and address to Tim Carter. Ask for Builder Bulletin No. 135.
You can obtain a free order form for a wide variety of individual job bid sheets and other available Builder Bulletins by sending a business-size, stamped, self-addressed envelope to the same address.
Ask the Contractor can also be accessed via the Internet at http://www.chicago.tribune.com/homes/articles/askcon.
