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topic 8715

Hot-Dipped Galvanizing Visual, Aesthetic Appearance


(2001)

I am interested in the aesthetic value of hot-dipped galvanizing. I have been told to expect a mottled color, & that an even grey color with this process is impossible. Is this true? I would like to see a galvanized object that has an even color & does not require a paint topcoat to make it look nice. I am well aware the protective abilities of galvanizing is not compromised by it's visual appearance, but that is not the question. Any information will be greatly appreciated.

Thanks.

Mark Taber
- Boston, Massachusetts


(2001)

Is that a mouse grey or pearl grey? Steel Chemistry will have the final word on what galvanized structural members will look like. Galvanizing is a zinc-iron alloy that can represent a wide range of "colors" based on ranges of steel chemistry (silicon, phos, carbon...). Of course galvanized sheet can provide more consistent coatings that can range in different spangles and appearances (galvannealed). A galvannealed coating would tend to be a flat grey color that is consistent. I guess it depends on your steel supplier and your part/ steel that you are using as to whether I could show you something that is consistent in color. Galvanized steel will change in appearance over time as the material "weathers." If you can be more specific of the part or application I might be able to speculate if you can achieve this "gray even color."

M Stroia
- Canton, Ohio


(2001)

Here are some of the specifics: Finish applied to structural members, not sheet steel. Uniform "frosted window" look desired, shiny not mat. What causes a matte grey finish instead of a shiny reflective one? Or a shiny surface mottled with matte grey? I don't have a reference for a 'mouse grey' vs. 'pearl grey', & need more info. to respond to that question. I appreciate your response.

Mark Taber
- Boston, Massachusetts


(2001)

Hot dip Galvanizing is an iron alloy layer comprised of different combinations of zinc and iron. The eventual appearance of the product will depend on steel chemistry of the product being galvanized, time of product in the kettle, and the retention of heat in the product after withdrawal. Silicon, Phosphorous, Carbon and Manganese in steel have the most profound affect that can lead to heavy and potentially brittle coatings if in excess (ASTM ASTM A385 [link by ed. to spec at TechStreet]). This coating will most likely be dull and frosty. When these levels are exceeded the iron in the zinc-iron alloy coating comes to the surface. When a product is brighter the pure zinc layer comes to the surface leaving a brighter coating. The pearl grey and mouse grey reference was a little sarcastic, since it is very difficult to project the result of a product without knowing steel chemistry or the product. Different galvanizers use different additives to the zinc bath such as nickel, bizmuth, aluminum, and tin to change the appearance of a coating and to aid in the types of products that they run in there area. The American Galvanizers Association can help you with some technical question as well as provide literature to explain this a little better.

M Stroia
- Canton, Ohio



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