Exfoliation Corrosion in Commercial Aluminum Roofing Panels

Exfoliation corrosion occurred on commercial aluminum roofing panels without any evidence of contact with corrosive media on the weather-facing exterior surface. Analysis revealed the corrosion initiated at the interface of the roofing panels and underlying plywood that was in direct contact with the aluminum sheet. No significant copper antifungal content was detected in the plywood; however, which is the typical culprit for galvanic corrosion of aluminum sheet in direct contact with treated wood. The corrosion was eventually attributed to a high phosphorous content in the plywood and the possible formation of phosphoric acid along the interface.