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Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2008

Painting Mild Steel Parts

Q: I am planning to make a large number of mild steel parts which need to have a finish to inhibit the formation of rust. I see many similar parts that have a zinc chromate finish and I am not clear what the enviroment impact of this process is and if there is a better, less polluting process we should consider.

A: Please tell me more about the parts you intend to paint. What are they? Where will they be exposed? There more information you give me, the better I can advise you.

Q: Wow, thanks for the quick come back. The parts are the steel pedestals that support raised floors, so the environment is “office”.

The current makers use a yellow zinc chromate finish, but I may have an advantage if I can come up with a satisfactory finish that is more environmentally friendly than a finish that has hexavalent chromium in it.

Perhaps Hot Black Oxide?

I am selling to some big contractors who have a corporate edict about the environment and are scared silly about bad press for sourcing parts that use polluting processes.

A: For an office environment you should not need to apply a zinc chromate primer since it is unlikely that corrosion will take place. On the other hand, if you sell the pedestals to office that are located in indoor humid atmospheres, perhaps corrosion might be a consideration.

A conventional red oxide primer should do well. Alternatively, there is a wide range on non-chromate primers on the market from which you can select. Call your favorite paint vendor and ask what primers he sells for mild steel.

If you apply the hot black oxide yourself, then go for it, but it is not something I would normally recommend because of the hazardous chemical process.

Good luck,

Ron Joseph

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