banyan sy

galvanic action in building science

Discussion created by banyan sy on Jun 7, 2019
Latest reply on Jun 15, 2019 by banyan sy

I have come into conflicting information regarding galvanic action as it applies to dissimilar metals.  As I understand it the anode is negative and the electric current flows from the negative to the positive cathode. I have come across a credible source Architectural Graphic Standards 12 edition that states in a chart a few confusing relationships (see first image).  Initially it states that the anode is positive, and the cathode is negative (see second image).  This is opposite as I understand it. Additionally, the chart states that if you were to use a copper flashing (building science element to control moisture in a wall at a windowsill for example) with stainless steel fasteners then galvanic action would occur.  However, it is my understanding that because stainless steel and copper are both rather cathodic, galvanic action would not be likely to occur. The chart also indicates that stainless steel and aluminum would not experience galvanic action yet as I understand it these metals are ‘far apart’ and therefor would cause a lot of corrosion of the anode aluminum if in contact with stainless steel. It is the 12th addition of a reputable source so…am I missing something? Please advise.Diagram from Architectural Graphic Standards 12th addition

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