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Great Expectations Evaluating the performance of UV-durable coil coatings by Scott W. Moffatt Photo © Steve Wanke Photography ALTHOUGH SILICONE-MODIFIED POLYESTER (SMP) AND SUPER-POLYESTER COATINGS ARE WELL-SUITED FOR SPECIFIC APPLICATIONS, THEY CANNOT PROVIDE THE SAME PROVEN LONG- TERM PERFORMANCE AS 70 PERCENT POLYVINYLIDENE FLUORIDE (PVDF) PRODUCTS. While many SMP and super-polyester coatings are excellent products well-suited to various architectural and building product applications, the practice of marketing them as comparable alternatives to 70 percent PVDF coatings may cause architects and specifiers to select the wrong product for their applications. This article examines differences between 70 percent PVDF, SMP, and super-polyester coatings, and explains why the first type generally retain its color and gloss longer than coatings based on the other chemistry. The basics Coil coatings are made from three basic ingredients: resins, pigments, and solvents. Resins Resins give coil coatings basic performance attributes such as resistance to abrasion, scratching, moisture, and ultraviolet (UV) light, as well as mechanical characteristics like adhesion, hardness, and flexibility during fabrication. Coil coatings are formulated with several resin types, including acrylic, epoxy, polyester, and PVDF polymers. For applications demanding a highly durable coating surface (e.g. metal roofing, composite panels, building panels, and curtain walls), 70 percent PVDF coatings are regarded as superior because of their strong UV resistance. Due to their lower cost and harder finishes, SMP and super-polyester coatings are traditionally favored for applications such as warehouses, industrial, storage, and agricultural structures, and other non-monumental commercial buildings. In recent years, some manufacturers have sought to position SMP and super-polyester coatings as viable, low-cost alternatives to 70 percent PVDF coatings. While it is true polyester coatings are more resistant to UV damage than early-generation coatings, they do not offer the same weatherability, color retention, and gloss retention as 70 percent PVDF coatings. 36 the construction specifier | march 2013 CS_Mar2013.indd 36 2/14/13 10:03:06 AM