Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2004

Paint Failure on Galvanized Roof

Q. A well-known coil coater company has denied a breach of warranty claim for rusting on a galvanized steel roof. Installed in 1992, the company claims that the rust is either the result of abrasions due to handling/ dragging by the installing contractor or acid rain. Parts of the same roof show no rusting whatsoever. The coating used on the roof panels was a fluorpolymer. Without more, can you give me an idea as to whether their claims are plausible? Thank you.

Thanks for your email. Without inspecting the roof it is impossible to speculate on the cause of the problem. It is certainly possible that the coating process was faulty, but one would need to examine the roofing in the failed as well as the intact areas to determine if there was a variation in the thickness of the galvanizing and/or the coating. The roof comprises many individual sheets of galvanized steel. Are they all the same? Do they come from more than one batch? Is the thickness of the zinc uniform throughout, (within industry standards)? Was the fluoropolymer coating uniformly applied on all sheets? Was the coating properly cured during its application by the coil coater? What is intercoat adhesion like? Is corrosion (zinc oxide) taking place under the fluoropolymer? Was the galvanizing properly pretreated before the coating was applied?

If the coater is correct, you would look at the roof to see if corrosion has indeed started at scratches and areas of physical damage. Clearly, if this is so, then the coater has a strong case. On the other hand, if you can demonstrate that there are inconsistencies in the roofing material (outside the normally accepted limits of variation), then you have a strong case.

If you want to pursue this my consulting firm can assist you. We work extensively on legal cases such as this. Unless the cause of the failure is visually obvious, it will take several hours of laboratory analysis to identify the problem.

Please fell free to call or respond by email if you want to take this further.

Best wishes,

Ron Joseph

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