Galvanic reaction occurs when two dissimilar metals come in contact in a corrosive environment.
The appropriate question may be, 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.
Caulking is often a fabrication afterthought—the last thing you do, so to speak, before wrapping up the project. In most cases, that is okay because most caulks are hardy, well-engineered and do their intended purpose. This is particularly true with steel, stainless steel and painted or coated metals.
However, if you have a project that requires aluminum, zinc, copper or brass, particularly the later three, you should pay attention to the specs and types of caulk being used. Again, it is uncommon, but there are types and brands of caulk that are better than others. Failed caulking, of course, can lead to bigger, even catastrophic, failures downstream.
Copper can eat through certain brands of caulk in very little time. If you have copper panels, as an example, on a building exterior or rooftop, combined with failed caulking a few years after the warranty has expired, it may lead to damage that costs a lot of money to repair without much recourse.
All Metals Fabrication has spent years developing core competencies in all types of metals.
We fabricate metal but even more, after nearly thirty years of experience, we understand the lurking problems that can happen when people are unaware or uninformed about important details.
Industry experience and quality of workmanship are vital. Fabrication choices—who you select as your vendor or contractor—should be made not only on price, but on the value of the offering. Less expensive will sometimes yield the opposite of the desired outcome.
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.
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