Repainting a rusting iron stairway

Q. I own a condominium apartment which has four iron outside stairways which are rusted. They have been scraped and repainted, only to rust again. Are there any factory-treated iron stairs that are rust-resistant? Would open wood stairs be desirable for a replacement? Are there any ready-made wood stairs or must they be custom-made? Ruth E. Preschby Chicago, Ill.

A. There may be factory-made iron stairs that are pregalvanized. Some may be or could be made of structural aluminum.

In my opinion, neither would be reasonable replacements for your merely rusting iron stairs. For a local answer and price to these possibilities, telephone a fabricator listed in the telephone Yellow Pages under ''Stair builders.''

I would not consider replacing the existing expensive iron stairs with wood ones which would have to be custom-made. In any event, they would have to be stained or painted and would also require maintenance.

Now about repainting the existing rusted iron stairs.

''Getting a paint job that will stand up for a few years on wrought-iron railing is perhaps as difficult as anything we have to do in the paint business, '' writes Donald Boysen of Frazee Paints & Wallcoverings, San Diego.

The reason, according to Boysen, is that there are so many sharp edges which make it difficult to get any film thickness on the edges substantial enough to protect the metal. In most cases, sandblasting is out of the question, so it is a matter of thorough sanding and scraping to remove the rust scale.

After the metal is clean, apply a package metal treatment, such as Trustan, or equal. Follow the labeled directions carefully. Let dry.

Next, apply two or three coats of a quality metal primer recommended by an industrial paint company. The key word is industrial. Ask for the material used to paint tanks and bridges. Accept only a top-of-the-line material.

Finally, apply at least two coats of a top-quality synthetic industrial enamel. Again, we emphasize the word industrial.

One last thing: Make the final enamel coat a reddish-brown color.