Don’t Mix your Metals

Let’s say you have a nice steel gutter system and one day something happens to one of your downspouts and it needs to be replaced…. So you call around and do some research and learn that aluminum is less expensive than steel and comes pre-painted, so you decide you want to replace the downspout with a new aluminum one – simple, right?
Yes and no…

Galvanic Corrosion is an electrochemical process which occurs when dissimilar metals are in contact with each other in the presence of an electrolyte, most commonly being moisture and oxygen. For example rain water and salt water make especially good electrolytes. An electrolyte could be any non-metal matter that will conduct an electric current and are predominantly liquids or moisture. Every metal has been rated for nobility and then placed on galvanic scales according to nobility. Basically nobility is a measurement of the resistance to corrosion, especially of one metal contacting another metal. Metals that are the least noble means they are very anodic, electropositive or high potential and will corrode most easily. Aluminum is the least noble, so it will corode the fastest. Metals that are the most noble, means they are highly cathodic, electronegative or low potential and will be the most resistant to corrosion. The most corrosive effects will occur between metals from the opposite ends of the galvanic scale or ranking of nobility. This difference in electrical potential between two or more metals causes galvanic corrosion. Dissimilar metals in contact with each other in the presence of an electrolyte causes current to flow through their points of contact at the expense of the metal with the higher potential or less nobility. The much less noble metal is gradually consumed in the Electro-chemical reaction and will deteriorate or wear away as the metal ions migrate away from the very anodic metal to the more noble cathodic one. The more noble metal’s corrosion resistance actually increases from this transfer of ions to it from the less noble metal, while the other metal is gradually getting consumed.

What does that mean?! It means that over time, with water flowing between the steel and aluminum, the aluminum is going to start to corrode and you will have a leak. This process speeds up near the ocean because of the salt water in the air. The good news is that we use bonderized or galvanized steel, which has a coating that prolongs the damage, and you can patch up a connection a few times before a whole section will need to be replaced. Also, if you are farther from the ocean, it will take longer for the corrosion to take place.So if you’re looking at the short term, it won’t be a big deal, but years down the line, mixing your metals can prove annoying and costly. It’s best to stick to one type of material in your gutter system if you can.

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