How to remove an anodized finish from aluminum

I'm working on a custom bus shelter that I would like to either powdercoat or re-anodize another color than what it is now. Unfortunately the shelter is a dark brown anodized aluminum color and I'm wondering how to get the shelter down to bare metal or remove enough of the brown color so that the new "green" color shows up well.

I've heard that acid etching works well, is that true?

"Acid etching" is a rather generic term that doesn't tell you much. Anodized coatings can be removed either with a mix of chromic and phosphoric acid or with caustic. The acid mix has the advantage of dissolving only the anodized coating, not the aluminum. But it sounds environmentally unacceptable to put chromic acid on an existing outside bus shelter; that approach only sounds good if you can bring the shelter to a plant for rework. Caustic dissolves aluminum as well as anodizing, so it must be watched carefully and rinsed away at the appropriate time.

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