Select the coating system carefully
There are several popular solvent-based options for exterior coating systems, ranging from acrylic latex and silicone-polyester formulations to two-component urethane blends and fluoroethylene vinyl ether (FEVE)-based resins. However, many in the architectural community have turned to single-component, water-based coating binder systems formulated with polyvinylidene fluoride (PVDF), which is a tough engineering thermoplastic.
The PVDF binder has many carbon-fluorine bonds that do not break down over time as do other polymers. This bond allows the coating formulation to withstand thermal, chemical, and ultraviolet (UV) conditions without losing thickness, providing proven weatherability in extreme conditions. The carbon-fluorine bond is very strong. The more fluorine a fluoropolymer coating formulation contains, the greater its performance characteristics. (For best results, water-based coatings are applied at temperatures above freezing.)
PVDF is naturally hydrophobic, so it resists or repels water rather than absorbing it. While coatings with other types of polymeric resins may have some initial hydrophobic qualities, this characteristic tends to degrade after about a year or two. Once moisture is absorbed into the coating, it hastens failure. While PVDF coatings inherently resist mold and mildew growth, fungicides can be incorporated to help further resist mold growth—a problem quite prevalent on architecture located in coastal areas or high-humidity environments.
PVDF-based coatings also resist UV degradation more effectively than FEVE-based coatings, two-component urethanes, and epoxies, which degrade faster, leading to chalking. Additional UV-blocking additives and complex inorganic pigments in combination with PVDF-based coatings further resist degradation from UV rays, which provides long-lasting fade resistance and protection of the substrate below.
PVDF coatings may not be appropriate for projects that require short-term protection or that have extreme cost constraints, and thus would not realize the cost benefits of a long-lasting, high-performance coating technology. Less expensive than FEVE coatings (also a fluoropolymer system), PVDF has a much longer track record (more than a half-century) of performance.
Side-by-side studies have been conducted on fade performance using the exact same inorganic pigments in both PVDF and FEVE resin systems. Panels were placed at a 45-degree, south-facing angle and weathered in South Florida. PVDF-based coatings proved to have better color retention in this environment.
Urethanes and epoxies are lower-cost coatings that have good performance on metal applications, but degrade faster and have a much shorter life span than PVDF and FEVE coatings. Color options do not vary between types of resin systems, but some coatings contain better quality pigments than others. One should look for coating systems that contain inorganic pigments as opposed to organic; such products should last longer in harsh UV-prone environments.
Conclusion
The proper exterior coating system will dramatically extend the life cycle of a building by resisting UV degradation, algae and fungal growth, abrasion, dirt pickup, staining, chalking, and mildew. PVDF-based coating systems provide a good solution for long-lasting performance. It is important to look for a coating system that offers a long-life guarantee, even for dark and vibrant colors, which tend to fade quickly in typical latex formulations.
Selecting a truly compatible coating system and a licensed coating contractor certified by that system’s manufacturer is a great start. Their expertise in selecting the right coating system to match the structure’s substrate, preparing the surface properly, and maintaining environmental compliance with local regulations will help ensure the success of the project.
Mike Couchie is the vice president of sales for APV Engineered Coatings. He has been with the company for more than 25 years, focusing on the commercialization and business development of high-performance coating technologies for building products, as well as other advanced materials ranging from OEM to field applications. Couchie received his degree in business administration from the University of Akron in 1990. He can be reached via e-mail at mcouchie@apvcoatings.com.
Ron Partridge is a senior account manager with Arkema Inc. He is responsible for Kynar polyvinylidene fluoride (PVDF) polymer products in the North American coatings market, and has worked for the company for 13 years. Partridge has three decades of experience in the polymer industry in sales, business development, technical service, and R&D. He received his degree in chemistry and materials science from the State University of New York (SUNY) at Stony Brook in 1984. He can be reached at ron.partridge@arkema.com.
