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Considering blackening of corrugated steel roofing

April 9, 2012

Q. I am a decorative finisher. A client and his architect wish me to consider blackening, partially, more like a patina, exterior corrugated steel roofing material.
The location is Sonoma County in California. The weather there ranges from much rain in winter to hot and dry in summer.

Is there a spray on type chemical process?product?

Will the steel,with this process react to rain e.g. rust?

Will oiling or waxing have beneficial effects?

Are there other considerations?

Thank you

Gregory Dixon

Gregory Dixon
- San Francisco, California, USA.

April 9, 2012

Hi, Gregory.

Rifle barrels and similar things that will be lovingly waxed and oiled at regular intervals are often black oxided. I can't imagine the process being even slightly successful as a roofing material. It would be expensive, but the sheets could be black chromium plated (like solar collectors). If the roofing were aluminum it could probably be anodized and dyed with some type on inorganic dye (integral colr, two-step, hybrid dye/two-step).


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

April 12, 2012

A. Hi Gregory,

It is possible to patina galvanized products. Ordinary "bluing" chemicals will do the trick, but I always advise against spraying them. You can also produce a "natural" zinc patina with cycles of salt water, air drying and mild acids. It takes some practice to control the look of the patina, but you can get some nice gray tones. Either way, this will not greatly affect the protection that the zinc provides the steel, but the patina itself probably won't last too long exposed to the elements.

Also, bear in mind that the zinc layer is usually protected by a chromate, you don't want this all over your shop, or in your waste water.

Neither wax nor oil will provide significant protection to the patina, unless you can convince the owners to reapply every few weeks or months... I have had some success with powder coating and some types of urethane. The surface would need to be clear coated immediately following the patina process and you have to be sure it is totally dry.

The short answer is, yet it can be done, but not easily.

Justin Kumpf
- Philadelphia, Pennsylvania, USA

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