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12/6/2018 Dan Paradela - Galvanic corrosion


     Galvanic corrosion causing excessive rust on newly constructed homes. On a recent inspection the rear balcony was improperly installed. First of all it had a negative pitch and was holding rain water. There was also metal to metal galvanic corrosion on the sheet metal floor covering, no nylon spacers were present between the bottom of the iron rails and the sheet metal. In addition improper fasteners were used to secure the rails and again no nylon washers were present to prevent galvanic corrosion. The house was not complete, yet already extensive rust was all over the beautiful rear balcony. To prevent these issues keep these things in mind.
     Galvanic corrosion is a process in which one metal corrodes preferentially when
it is in direct contact with another, in the presence of an electrolyte usually rainwater or groundwater. When a metal atom is oxidized it leaves its bulk metal after losing one or more electrons and is then transferred to another site. The site where the metal atoms lose electrons is called the anode,

while the site where the electrons are transferred is called the cathode. Use a galvanic series list of metals to determine which are the best metals for your project. The metals on the anodic, or less noble end will corrode faster than the metals toward the cathodic, or more noble end. It is especially important to consider the potential of galvanic corrosion when choosing metal paneling, trim, and fasteners. When choosing materials, choose metals close together on the list, as metals close together will not have as strong of an effect on each other. The farther apart the metals are on the list the stronger the corrosion on the less noble metal. You can also use nylon spacers and washers or sacrificial anodes including sacrificial metal coatings depending on the application.