Metals
When two metals of differing electro-negativity values come into contact in humid conditions, an electrical couple is formed giving rise to oxidizing effects at the expense of electro-negative metal of the couple. In order to avoid severe corrosion effects, an insulating barrier should be placed between the two metals. Contact with stainless steel has not been found to be harmful to aluminium to date. Contact with copper and its alloys is extremely harmful to aluminium. It is absolutely necessary to insulate these two metals. Lead should be insulated as well.
Timber
Most timbers have no harmful effects on aluminium. Some such as walnut however, produce acids which attack and damage aluminium. These effects occur especially in humid conditions or when the timber is not sufficiently dry. Insulation is recommended by using a bituminous paint. When you treat timber against humidity and insects you should check that the chemical substances used in the treatment are not harmful to aluminium. Products containing copper salts, mercury salts, and fluoride compounds are very harmful to aluminium and should be avoided.
Lime/Cement
In humid conditions, limestone or cement reacts with aluminium (even when anodized) revealing superficial white spots on the surface of the metal after cleaning. It is advisable to protect the aluminium during installation with protective foil.
