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Powdercoat or Stainless steel panels better for resisting moisture

Q. Greetings, I am a job shop owner (steel fabrication) as well as a Mechanical Engineer. I have been hired to purchase and install the following... Here is the situation. Customer desires perforated sheet material hung overhead in lew of a "normal" ceiling/ false ceiling. There is approx. 1000 ft^2 that needs to be covered. (not a small area.) The area being covered is outside. There will be no direct water sprayed on the panels, but there will be moisture/ humidity from the elements.  The desired asthetic look is a somewhat dull, brushed stainless (#4 finish?). However, they were shown a sample of cold rolled steel, clear powder-coat and were happy with that.

The main question:
1. Will the clear powder-coating hold up over the cold rolled steel? (cheaper than SS)
2. If we go with 304ss, #4 finish do we need to passivate/ electropolish after to be sure that the material will not "rust"?
3. What about AL? Clear ano?
4. What material coupled with what process will hold up best with time and still match the given desired asthetic look? Thanks for your time!    

Cary McCune
design - San Luis Obispo, California, USA

A. Some of the most basic tools the metal finishing industry has developed over the decades for fighting corrosion of steel--like phosphatization, and e-coat primers--would seem to be incompatible with a clear coat that lets the steel show through. So I would be leary of that one for any outdoor exposure at all.

I think I'd go with the anodized aluminum.

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


A. 1. I agree with Ted on being leery of the clear coat. Coatings of this type are notorious for discolorations and peeling in the sun after awhile. I would only use it if the supplier is willing to guarantee it and replace it if it discolors and/or peels; because you will have a mess if it does. You could look at the exterior stability of the particular plastic material being used in the powder coat to see if it will hold up.

2. You certainly must passivate the surface at a minimum to ensure that it will not rust. If it is anywhere near the ocean it will not hold up long term in all likelihood. Need 316 then.

3. Ano. aluminum could work in CA.

4. With the sun in CA I would avoid any plastics. Either alum. or stainless steel.

lee kremer
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Lee Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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