Yes, you can apply TotalBoat Polyester Structural Repair Putty to metal as long as the metal surface has been prepped properly. Having said that, even though Polyester Structural Repair Putty can bond to metal, application to metal is not a common usage for it. If you do apply it to metal, note that it doesn't contain any wax or air-dry additive - you'd need to apply PVA or some other type of air-dry agent to make the putty cure properly.