Comparing Metal Coatings: Anodizing, Paints & Powder Coatings
The right surface coating or finish on your commercial metal railings and other architectural metals can define the look of the system and play a critical role in the longevity and performance of the metal. Metal finishes can not only improve the appearance of the metal but can also dramatically affect such factors as corrosion and overall wear resistance.
Determining the right coating for the project and application is a critical project decision and design element. This article provides an overview of the three most common types of metal finishes and coatings: Anodized metals, painted metals, and powder-coated metals.
Anodizing is an electrochemical process that forms a protective coating of aluminum oxide on the metal surface. This creates a decorative, durable corrosion-resistant finish. Aluminum is most often used, but the process can be applied to other metals such as aluminum alloys, titanium, and stainless steel. The anodizing process doesn’t coat the metal, but instead integrates the oxide finish as a part of the metal itself. Accordingly, the surface will not chip or peel. Anodizing can be used to create both colored and clear metal finishes.
An anodized finish is more common with aluminum metal products is typically less expensive than painting. It’s harder than Polyvinylidene Fluoride (PVDF) or Fluoroethylene Vinyl Ether (FEVE) and better for aluminum applications in high-traffic areas where the finish is subject to everyday use and abrasive cleaners. Anodizing cannot peel off as the coating is actually part of the metal. An anodized coating is translucent over the base metal, which gives the aluminum a deeper, richer metallic appearance than organic paints. However, the translucence can contribute to color variations. Anodizing is not affected by UV or sunlight whereas organic coatings can be susceptible to UV degradation.
To see how the anodizing process works, view GRECO’s “Finishes & Coatings” YouTube playlist to view Hydro’s video “What is Aluminum Anodizing and How Does it Work | Anodizing Process Overview.”
Paints and Powder Coatings both fall under organic coatings. The performance of an organic coating depends on the type of pretreatment, the resin used, and the pigmentation. When applying to aluminum, the pretreatment is critical. As such, organic coatings should always be applied in a controlled factory environment.
The resin used in organic coatings is the most important component. There are many types of resin available for architectural applications, such as Acrylics, Urethanes, Polyurethanes, Polyester, Silicon Polyesters, and PVDF to name a few. PVDF is one of the few coating systems that will last for more than five years and, consequently, one of the most common systems used in architectural metal applications. Kynar 500® is a PVDF resin that many designers are familiar with due to its outstanding performance.
The American Architectural Manufacturers Association (AAMA) has several excellent performance specifications for aluminum coatings with AAMA 2605 being the most stringent specification for spray coating used in architectural metals. (AAMA Specification Table).
An important aspect of the AAMA 2605 standard is the requirement for actual ten-year exposure in South Florida. It is a good idea when evaluating different coatings to request the results of Florida exposure. PVDF coatings have been shown to pass AAMA 2605 in the widest variety of colors. Remember that AAMA 2605 is only for spray coatings.
PVDF coatings are usually formulated as 70% PVDF and 30% other resins, acrylic usually predominating. While 50% PVDF coatings are available, they do not meet AAMA 2605 but will meet AAMA 2604, which is considered an intermediate specification. Chemical resistance and resistance to UV light are the strengths of PVDF coatings.
PVDF is an inert chemical that will outlast anodizing in corrosive environments, offers nearly an unlimited selection of colors and can be manufactured in small batches. Color consistency is usually better than with anodizing, however, it is typically more expensive.
PVDF is produced by two firms: Arkema Inc and Solvay Specialty Polymers. Solvay’s Hylar 5000® and Arkema’s Kynar 500® are their respective brands. Today, Kynar 500® is exclusive to PPG Industries (used in their Duranar® fluoropolymer coating), and Hylar 5000® is used by; Valspar, Sherwin Williams, and Akzo Nobel.
PVDF coatings have dominated the architectural metal market due to its color consistency, color selection, abrasion resistance, and overall weather ability. With PVDF, a specifier may choose any color he or she wants, and it is likely to be readily available since most applicators have the capability to mix their own coatings.
POWDER COAT METAL FINISHES
Liquid paint is composed of pigment, resin, and solvent. Powder paint is simply pigment encapsulated in a powdered resin and is thus simply thought of as “Paint without the solvent.” Powder coatings and liquid coatings made from the same resin and pigment will have practically the same performance characteristics. For a given resin, the decision to use a powder or liquid coating is mainly a question of application technique.
Powder coating is achieved by applying an electric charge to the metal which allows a dry powder fuse to the metal’s surface. It is then baked in a curing oven to result in a smooth coating with a finish more durable than conventional paint. Powder coat finishes are commonly used with aluminum, but can also be applied to steel and stainless steel products.
Powder coating is an ideal choice for companies focused on sustainability and/or achieving green building certifications. Powder coating releases nearly zero volatile organic compounds (VOCs) into the environment and creates zero hazardous waste on job sites.
Aesthetically speaking, it is easier to achieve a uniform or consistent metal finish using powder coating techniques. It’s also highly customizable, making it perfect for pops of color in buildings where clients want to feature company brand standards and/or make the architectural railings complement the area’s natural landscape. You can view the diverse powder coating color options available by referencing the classic RAL color system.
This metal finish is durable and budget-friendly with larger quantities as the process is very specific in the materials needed. There is hardly ever any waste associated with powder coating, and it’s recognized as high performing with low maintenance costs.
So, then why doesn’t everyone select a powder coat metal finish? The answer is simple: The organic powder coat finish cannot withstand the same abuse as its inorganic counterpart, anodizing.
To see how the powder coating process works, view GRECO’s “Finishes & Coatings” YouTube playlist to view Hubs video “What is Powder Coating and How Does it work?”
RECOMMENDATIONS FOR METAL RAILING COATING
When evaluating the various finishes for commercial railings or architectural metal products, you will need to weigh the performance, aesthetics, and cost. Early communications and collaboration with GRECO Architectural Metal Products can eliminate costly mistakes and any misunderstanding related to finishes, and deliver the right finish for the job.
GRECO designs, engineers, manufacturers, and installs all of their architectural railings and metal products. As an industry leader, GRECO offers innovative designs, outstanding customer service, and unparalleled technical support. Contact GRECO for help on your next project.