Doright wrote:Aluminum has a Clad coating on it, This Clad is a coating of pure Aluminum which oxidizes instantly when exposed to air. It protects the base Aluminum, When you sand it you break through it very easily once the Clad has been removed the Aluminum starts oxidizing instantly and because of that its a good idea to treat the Aluminum with AlumaPrep followed by a treatment of Alodine which can then be painted with a Good coating of Zinc Oxide Primer followed by BC/CC or SS this would be the process for restoring the coating on most all aircraft.