While you might think that metals like galvanized steel, copper and aluminum will last forever, there are certain circumstances under which they will corrode. The trick is to avoid those situations.
Refined metals are unstable, and can be affected by interaction with other metals and materials. And that can lead to real problems when it comes to working around your house.
For example, some older homes may still have galvanized steel water pipes. Maybe you want to repair a section with new copper pipe, but you don’t want to pull out the whole section. Just attach the copper to the steel with a copper fitting, right? Stop right there. Galvanic corrorsion will likely occur, and your nice repair job will soon be leaking all over. Use a brass or plastic fitting between the two metals instead.
Likewise, don’t drive galvanized nails into copper flashing.
Taking a lesson from above, using copper counter flashing (or cap flashing) over aluminum step flashing is also a no-no.
This will also affect the type of solder and flux you use when soldering these metals.
Metals can also react with other substances. Coated aluminum — which is often a great material to use for flashing, soffits and eavestroughs — should not be used for counter flashing when the flashing is embedded in mortar in a brick wall. While the aluminum is coated, the alkalinity in the mortar will attack the cut end and quickly corrode the aluminum.
So, before you put any two metals together, make sure they’re suitable partners.