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Protection of punched areas of GALVANNEALED (A60) material

I'm a mechanical designer. At our company we manufacture pre-fabricated weather-proof metal buildings. My question is, after we punch holes in our galvannealed (A60) panels, we deburr the punched area with a small hand sander (180 grit). I am concerned that we are damaging the A60 coating, please comment.

Ronald E. Davidson
- Canton, Ohio

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You're not damaging it, Ronald, you're completely removing it from the punched areas. In benign environments that's not a big problem because the ganvanneal can sacrificially protect the exposed steel. But with the environment that a roof sees, and the probable retention of moisture under the fasteners, it's not a good situation. I would protect the exposed steel surfaces with cold galvanizing compound Cold Galvanizing Compound / Zinc Rich Paint, or somehow -- with lacquer, paint, mastic, or something.

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

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