Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2004

Painting Steel Roof

Q. About six years ago, we had steel roofing applied to the portico and around the top of our commercial building. The paint has faded and oxidized. Our handyman attempted to paint it using a white latex primer and red latex overcoat with obvious results. The primer has bled through the red paint and it is blotchy and has many runs. I suggested that latex was not the appropriate type of paint and that the surface should have been prepped and cleaned before painting. Do we need to sandblast the latex off the surface and start over? What type of primer should we use and what type of top coat should be used for best results? Does the primer coat need to be sanded before applying the top coat(s)? When using red or maroon paint should we use a gray primer as opposed to white?

Your statement about the surface being prepped and cleaned before painting could not have been more accurate. The finish will only be as good as the surface preparation work. If the quality of the prep work is marginal, then too will be the quality of the paint finish.

If the latex primer is intact, and adhering well to the surface then I would say that surface blasting is not necessary. I do recommend that the area be properly prepared.

Clean the intended surface with a pressure washer and mild detergent to remove any oil, grease or dirt. Remove all old peeling paint by scraping with a putty knife or with a wire brush. Feather out any sharp edges with sandpaper, abrade the entire surface either by sanding or wire brush in order to create a good clean surface for the paint to adhere to.

When preparing any surface for the application of paints or coatings, be certain to take precautions to protect against breathing in any air borne dust or debris that may be created by the prep work. Pressure wash the entire surface once again to remove any additional dust or debris created by the prep work.

There are several high performance waterbase products available that are especially formulated for this type of application. Consult with your local paint supplier, inform them of your intentions and request specific product and application recommendations. They should have the products and colors available that will meet your requirements.

Please be aware that paints, coatings and solvents are chemicals and therefore you should always pay attention to proper handling procedures and be prepared to wear protective clothing, such as respirators, gloves, coveralls, etc. For further information on the health and safety requirements for the coatings and solvents you wish to use we strongly advised you to contact your local coating supplier. If possible, go the extra step and look for this information on the website of the product vendor.

Regards,

Jim Burke