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Question posted - February 28 to March 5, 2016:

If an atmospheric coating system of a zinc-rich epoxy, epoxy mid coat and polyurethane color topcoat has properly cured with no visual defects, should I be worried if the thickness of any coat exceeds any specified maximum?

Selected Answers

From trevor neale of TF Warren Group on March 4, 2016:
There are too many variables to give a definitive answer. If the coating is in a benign area with little temperature variation, you should probably not be worried; however, the exothermic reaction during the cure can cause unwelcome stresses in some epoxies applied at higher than specified DFTs.  Only the coating formulator or manufacturer is qualified to give a true answer.

From Robert Ikenberry of California Engineering on February 29, 2016:
The short answer is probably not. I am assuming this question is being asked from the owner's perspective. The full answer, as always, begins with "it's complicated." If there is a specified maximum per coat and it is exceeded, the specifications have not been met and the coatings could be rejected, but this is probably not in the best interests of all the parties if there are no visual defects (and there were none during the application). Accepting the coatings is certainly the simplest approach. It avoids delays getting equipment back into service, avoids litigation expenses, and is generally not likely to cause major service issues. Ask the coating manufacturer to confirm they will stand behind the coating as-applied, and document the non-conformance, so if there is a failure tied to thickness during the warranty period, it is clear where the responsibility lies. Most coatings will show visual defects if the recommended thicknesses have been significantly exceeded. Zinc rich coatings will mud-crack, overlying coats will pinhole, or the finish coats will have runs and sags. If none of these over-thickness problems evidence itself, service problems are unlikely. Over-thickness could be a problem if the coatings are subjected to excessive thermal cycling or extreme vibration, or it could play a part in inter-coat adhesion issues long down the road when overcoating. Otherwise, you probably don't need to worry.

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Tagged categories: Coating / Film thickness; Coating/Film Thickness; Coating/Film Thickness; Epoxy; Polyurethane

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