Galvanic reaction occurs when two dissimilar metals come in contact in a corrosive environment. So what does this have to do with caulk? You may be surprised to learn that some silicone caulks and sealers can release acetic acid during curing, which can react with certain metals and cause a galvanic reaction to caulk.
Caulks are made from one of four base polymers—latex, polyurethane, rubber, or silicone—which determines what materials they will adhere to. Whereas sealants are used in many metal fabrication applications regarding seams (such as roof expansions, roof to wall transitions, and gutters) to allow for metal expansion and contraction, caulks are more rigid and are typically used where there isn’t as much movability, to prevent dust and moisture from seeping in. Galvanic reaction to caulk is dependent upon the type of metal used.
Silicones are popular because of their superior adhesion to certain metals, such as steel. There are two types of silicone caulks: acid cure and neutral cure. Neutral-cure silicones are used successfully in metal fabrication projects. Acid-cure silicones, on the other hand, can have a corrosive reaction with galvanized metals.
How does this all work? According to Silicones: Chemistry and Corrosion, “Single part silicone sealers generally contain a cross-linking catalyst (such as a tin compound) that is activated upon exposure to moisture in the air.” When acetic acid is released, it attacks and corrodes metals such as copper, zinc, brass, and galvanized steel. In addition to causing galvanic reaction, it also prevents proper adhesion of the silicone to the metal. On the other hand, acid-cure silicone can etch the surface of aluminum and increase adhesion.
The best way to prevent galvanic reaction between caulk and metal is to know the chemical properties of the caulk as well as the properties of the metals to be used in a fabrication project. All Metals Fabrication has spent years developing core competencies in all types of metals. Our engineers and fabrication/installation crews are true craftsmen, OSHA trained, and certified in their respective fields, so you can rest assured that your metal fabrication project is done right.