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Ask the Builder: The right paint for your rusty steel

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By Tim Carter
Washington Post Staff Writer
Saturday, May 15, 2010

DEAR TIM: Painting some rusty steel is on my to-do list. Does anti-rust paint really work? I haven't had much luck in the past. Any tips you can share would be greatly appreciated.

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-- Sandy P., Greensboro, N.C.

DEAR SANDY: I've had lots of experience painting rusty steel and iron. Over the years, the different paint products I've used have changed -- however, I continue to have great success keeping metal from rusting.

If you travel much, you've probably seen rust-stopping paint in use on highway bridges. Rust is a major headache for these structures, as well as for countless other buildings and towers exposed to the weather. Because steel is such a strong and affordable building material, it's used everywhere. The trouble is that when left unprotected, it wants to oxidize, forming the rust that can weaken it and affect its appearance.

For years, the coatings industry has been developing incredible paints to protect steel from rust. Any decent paint store today will have rust-preventing paint in stock. Often, the trick is to use a special primer that's meant to be used on bare steel or steel that may have a fine coating of rust. These primers are developed to bond well to oxidized steel. That's what you want -- a great bond between the steel and the paint -- and that's what certain paints are designed to create.

You've probably heard of the popular national brand called Rust-Oleum. I've used it for years with great success. This is a consumer-brand paint that can be found in just about every hardware store and home center. It comes both as a spray and as brush-on paint. I've used both with fantastic results.

Here are some tips: Always read the label on whatever paint you decide to use. Make sure you can paint the object correctly. Some paints and rust-inhibitor paints need the steel to be rust-free. Other paints will work with some rust present.

The instructions on the label almost always call for you to scrape off any flaking rust or metal scale. This is just common sense. The better job you do preparing the surface, the longer the paint will last.

Pay attention to the temperature guidelines as well. Don't paint in extreme conditions where you're at the limit of the paint's tolerances. Take your time and be sure you coat the surface of the metal completely.

Avoid skipping steps. If the finish paint you intend to use requires a special rust primer paint, use it. Don't try to substitute a different primer. Many finish paints are formulated to bond to primers made by the same company.

Read the section on the paint label about recoat times. It's always a good idea to apply the finish paint as soon as you're allowed. When you do this, the finish paint can bond both chemically and mechanically to the primer.

Whenever possible, I like to paint steel with a spray gun. It takes some extra time to set up to prevent over-rust paint spray, but in the long run it can be a time saver. If you decide to use spray equipment, make sure you don't thin the paint excessively. Too much thinner will weaken the paint.

Tim Carter is a columnist for Tribune Media Services. He can be contacted via his Web site, http://www.askthebuilder.com/printer_submit_question.shtml.

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