Ask the Expert Question-and-Answer Archive

by Ron Joseph

April, 2009

Painting Outdoor Structure

Q. I am wondering if you can give me some directions and/or recommendations to few paint products that are suitable to finish a structural steel structure that is not galvanized, and currently open to landscape, so application method would need to be sensitive to overspray and air pollution control.

The structure is an atrium like structure with a metal roof on top. Columns and certain roof members will be exposed to weather. I like to find a paint that is ideally low voc and corrosion resistent.

I thought about epoxy paint, but I am not sure whether it can be sprayed in the outdoor enviroment or would brushing or rolling the paint is my only option.

A. If you are concerned about spray painting in the open environment, you should not use an epoxy or a polyurethane, because the overspray can settle on cars in the neighborhood and these coatings are extremely difficult to remove. Unfortunately, small paint particles can travel relatively long distances before they settle.

You should consider a waterborne coating system, comprising a waterborne corrosion resistant alkyd primer followed by two or more coats of an acrylic latex.

You didn't mention how you plan to prepare the steel surfaces prior to priming. This can make all the difference in selecting your coating system.

The system I recommended should not be expected to give you long corrosion-free life unless the steel is very well prepared using a phosphate pretreatment system. Unfortunately, since the atrium-like structure has already been erected, it is too late to send the steel off to a custom coating shop where the pretreatment could be carried out. This is not something you can adequately perform on site.

If you are willing to brush or roll the coatings, you can consider the epoxy/polyurethane option and can expect better life than the alkyd/acrylic option I mentioned earlier.

All coatings should be low VOC since hardware stores and paint stores are obligated to sell low VOC products, depending off-course on the state in which you reside.

I hope this helps.

Regards,

Ron Joseph