Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

September, 2003

Painting Metal, Steel Doors

Q. What type of paint is best for painting exterior metal doors. I'm concerned about repeated exposure to excessive heat. Are there any coatings, such as, polyurethanes or spar urethanes that can be applied over latex paint to provide added protection.

A. I'm assuming that you are painting steel doors. A good high quality exterior latex paint will do an excellent job on these exterior doors, providing that the metal surface was prepped well prior to the application of the paint top coat. Any paint job really is only as good as the prep work done prior to the application of any paint. Considering the last statement, and to answer your question more directly, if you prepare the surface of the existing latex paint by sanding, and cleaning it well, you should be able to apply a high quality exterior grade oil base paint to the doors in question. This will only serve as a protective coating for the latex paint, and not improve the adhesion properties of the coatings system to the surface of the doors.

If you are painting over aluminum doors, then you will need to be more careful with the surface preparation of the aluminum. The comments that follow apply only to those areas in which the bare aluminum metal is showing through. The comments do not apply where you are applying fresh paint over old paint.

Aluminum is a very difficult substrate to paint successfully. In professional circles companies go to great lengths to prepare aluminum before painting because paints and coatings do not adhere easily to the surface. Please be warned that my suggestions below are not guaranteed to work. I am only offering these suggestions in the hope that you will get by.

Thoroughly sand clean and wash the bare aluminum surfaces. Be sure that there are no contaminants left behind by the stripping process. Purchase an acid etch "wash primer" from an industrial paint store and ask the folks there for directions to apply the wash primer to aluminum. The instructions are different for aluminum than for steel.

If the folks at the paint store don't know the difference then call the paint company and get directions from the technical folks there. Once you have prepared the aluminum properly, you can repaint the remainder of the doors exactly as described for the steel doors.

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