Sep. 08, 2025
Anodizing | Organic Coatings | Recommendations | Conclusions
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The purpose of this article is to help you decide what type of coating to use — anodizing, paint, or powder coating when specifying architectural aluminum, whether the application is metal roofing, storefront, or curtainwall. The application and desired appearance dictate the finish selected. You may also go directly to How to Specify Anodized and Painted Finishes for more direct specification information.
Anodizing is a simple electrochemical process developed 100 years ago that forms a protective coating of aluminum oxide on the surface of the aluminum. The lifetime of the finish is proportional to the thickness of the anodic coating applied.
Aluminum oxide is a hard, durable, weather-resistant substance that protects the base metal. The coating may be colored by dyeing or may exhibit bronze tones through diffraction phenomena produced by the coating. The coating grows from the base aluminum metal by this electrochemical process. The coating is integral to the metal and can not peel or flake. The structure of the coating is many small hexagonal pores, which are filled with a “seal” that hydrolyzes these pores to fill them with inert aluminum oxide.
Anodizing that is improperly sealed has poor chemical resistance. Brand new anodizing with a thin coating thickness is nearly identical in appearance to an Aluminum Association Class I (very thick!!) anodized finish, but thin (sub-Class II) anodized coatings are unsuitable for use on exterior curtainwall or metal roofing.
The advantage of a thicker anodic coating is its durability and longer life. The Achilles heel of anodizing is it’s chemical resistance. Eventually, the surface of an anodic coating may succumb to acidic pollutants in urban environments. Anodized surfaces, like other building components, must be protected from acidic attack during construction. The life expectancy of an anodized coating is determined by its thickness and the building’s environment.
After many years anodized surfaces may accumulate dirt and stains that look similar to chalking paint. This “chalk” can be removed with a mild detergent combined with an abrasive cleaning technique. A small amount of the anodic coating can actually be removed, leaving behind a renewed anodized finish which can last for another twenty years. This is why anodizers say their product is “renewable.” Once an organic coating has failed, the only options are to re-coat the surface with another paint or replace the metal. When an anodized coating appears to have failed, cleaning often results in a renewed appearance.
Anodizing appears to be compatible with today’s environmental concerns. Though more research needs to be done to determine the total environmental impact of different aluminum finishes, from a finisher’s point of view, compliance with environmental regulations is easier than with other metal finishing processes. There are anodizers positioned in every major urban area, and anodizing may help products qualify for LEED (Leadership in Energy and Environmental Design) points based on regional materials.
The chemicals from anodizing can be used by municipal wastewater treatment facilities. The aluminum sulfate from anodizing plants’ effluent actually improves the solids settling efficiency of some wastewater treatment plants. Anodizing byproducts are often beneficial, like when aluminum trihydrate is often used as a fire retardant. Anodizing emits no ozone-producing solvents (VOCs), and there are no heavy metals involved in the process.
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The performance of an organic coating (paints or powders) depends on the pretreatment, resin, and pigmentation. With aluminum, the pretreatment is of utmost importance. This is why organic coatings for aluminum should be factory applied. Resins are often the weak link in an organic coating system. Some resins, such as PVDF, have outstanding weather-resistance, while epoxy coatings are meant only for interior use. There are many resins available for architectural use such as Acrylics, Urethanes, Polyurethanes, Polyesters, Silicon Polyesters, Polyester TGICs, PVDF, etc. Only a few of these coating systems will last for more than five years in exterior architectural applications. The American Architectural Manufacturers Association (AAMA) has several excellent performance specifications for aluminum coatings, and AAMA -17a is the most stringent specification for spray coated aluminum used in architecture. See AAMA Specifications for Painting Architectural Aluminum overview table here.
An important aspect of AAMA -17a is the requirement for actual ten-year exposure in South Florida. It is a good idea when evaluating different coatings request the results of Florida exposure. PVDF coatings have been shown to pass AAMA -13 in the widest variety of colors. Remember that AAMA is only for spray coatings. The right specification for coil-coatings is AAMA 620. Because coil coated processes tend to be more tightly controlled, longer-term warranties are available.
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 in as many colors. Chemical resistance and resistance to UV light are the strengths of PVDF coatings. PVDF has come to dominate the curtainwall and metal roofing markets because of its weather resistance, and because of the wide variety of colors available.
PVDF is produced by two firms: Arkema Inc and Solvay Specialty Polymers. Solvay is promoting PVDF under the trademark Hylar ® and Arkema Inc uses the tradename Kynar 500®. Today, both Solvay Specialty Polymers and Arkema are providing PVDF resin to the four companies qualified to mix this special coating: PPG Industries, Valspar, Sherwin Williams, and Akzo Nobel. There are also PVDF resins imported into the U.S. which are not Kynar or Hylar. This is why throughout this article, we have referred to these resins as PVDF whenever possible.
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.
The real advantage of powder is the reduction in air pollution compared to liquid coatings. When powders are cured in an oven, they emit no VOCs. A disadvantage of powder is the large batch sizes that are typically required. The powder manufacturers are aware of this problem and a few of them keep colors in stock that they distribute in small batches. Several companies manufacture exterior grade powders using a Polyester TGIC resin. Polyester TGIC powders are currently available in more stock colors than any other powder. Several companies stock hundreds of colors of Polyester TGIC powders. Polyester TGIC struggle with gloss retention compared to PVDF powders, but are widely used in Europe.
Some resins are more easily manufactured in liquid coatings, and some are more easily manufactured in powder coatings. A particular resin is usually manufactured in either powder or solvent-based coatings, but not both. Examples of this are epoxy which is predominantly a powder coating, and PVDF which historically has been manufactured as a liquid coating. Many of the perceived advantages of powders over liquid coatings such as hardness and gloss are actually characteristics of the resin.
Powder coatings from most manufacturers are only available in large batches, and custom colors can be very expensive. This is because each batch of powder must be ground to order using costly grinding equipment. Solvent born colors will continue to maintain their niche in the market because of the ease with which small batches can be mixed. The ability to “mix and match” gives painters and their customers unequalled flexibility and ease of use.
During the last fifteen years, PPG, Akzo, and others have introduced AAMA fluorocarbon-based powder coatings. Most of these are based on FEVE resins which are superior to Polyester coatings. PPG has introduced the PVDF Duranar powder which offers not only AAMA performance. It is also practically identical in appearance to liquid PVDF coatings. We expect the use of AAMA powder coatings to increase.
SAF also applies epoxy-based powders for interior applications such as furniture. One note of caution about powders: they are prone to orange peel, and the coating may appear to be textured.
Click to review our own SAF Painting Guidelines for Aluminum Finishing.
Resins can theoretically be made in either solvent-born or powder coating formulations. Some resins are easier to manufacture and/or apply using solvent-borne formulations, but solvents cause air pollution. The force of regulation weighs heavily on the construction industry, especially on solvent-borne coatings. Solvent-borne coatings for long-term exterior architectural applications are mostly solvent-based where typically between 70 and 80% of each gallon of paint is evaporated during the paint curing process. Included in the fumes are hydrocarbons which are termed VOCs (volatile organic compounds) by the EPA, and are a precursor to ozone formation similar to automobile exhaust. Ozone is a major component of smog and can cause eye, lung and throat irritation. Regulations such as the Resource Conservation and Recovery Act (RCRA) and the Clean Air Act will reduce ozone formation, although local action plans vary widely. If Southern California is an indicator of future environmental regulations for the rest of the country, it may soon be illegal in the U.S. to spray many solvent-based coatings including PVDF without costly environmental equipment. This is driving up the cost of solvent-borne coatings.
Organic coating manufacturers may be forced to decide between recommending their applicators install costly pollution control equipment, or developing powder coating technology. Powder coatings produce no air pollution and are becoming full-fledged competition for anodized and solvent-borne coatings.
In order to qualify for the longest spray-coat warranties, the major PVDF coating suppliers still call for chrome-based pretreatment. A chrome pretreatment is required for long-term adhesion for exterior use, but it requires that applicators have extensive water pollution control equipment. While this technology is well known and produces excellent adhesion results, the sludge from this process is a hazardous waste and is difficult and costly to dispose of.
In light of these new developments, specifiers may wonder what the best way is to specify a long-lasting painted finish. Our advice is to consult with your finisher, specify AAMA , and to rely on the expertise of coating manufacturers like PPG, Akzo or Valspar who mix these coatings for the architectural market.
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PVDF coatings have dominated the curtainwall and metal roofing markets because color consistency and color selection are more important than abrasion resistance. With PVDF, a specifier may choose any color he wants, and it is likely to be readily available since most applicators have the capability to mix their own coatings.
In most situations, PVDF coatings exhibit excellent color consistency. This does not mean that color consistency is perfect with paint. Contractors must be careful to have their metal coated at the same time in the same place whenever possible to reduce the probability of color variation caused by different batches of paint or application conditions. Often there is severe color variation with three and four coat metallic PVDF coatings. Architect’s objections to metallic paints are reminiscent of their objections to anodizing. For more information about color variation follow this link.
Care must be taken when applying touch-up paints because a perfect match is impossible between the factory-applied finish and a finish applied in the field. Touch-up paints are a problem for both painted and anodized coatings. Touch-up paint should never be sprayed on but touched on lightly with a brush. Touch up paint will fade and chalk at a different rate than the underlying coating.
When a lively, translucent building exterior is desired, anodizing is a good finish for curtainwall. Architects should require color range panels from the anodizer. The installer should be aware of the variability expected from anodized panels. An installer may be able to sort some of the panels by elevation for the desired effect. Sorting may also be required with metallic painted coatings. If a panel is outside the approved color range, the finisher should not ship it. Importantly, it is also the installer’s responsibility to avoid installing metal that is not within range. When specifying anodizing for monumental use, be sure to specify SAFINISH (Aluminum Association Class I). Follow this link for an explanation of Aluminum Association Designations.
The reason for specifying SAFINISH anodizing (Class I) is to make an anodic coating as durable as possible. Coating thickness is the most significant indicator of durability for anodized coatings. Coating thickness for architectural use can be specified as either Class 1 (0.7 mils) or Class 2 (0.4 mils) per Aluminum Association DAF 45, but often there is no specification. The “cheapest thing” is then installed, and in a few short years, the finish is pitted, stained, and eroded.
Cheap anodized sheets are often sold with a coating thickness of 0.10 mils. A finish of this thickness also might be called a 200, A21, A22 or A24. While this coating thickness is suitable for many applications, specifiers should know that the integrity of this finish will not last more than a few years in exterior architectural applications. The expected lifetime is much less in coastal environments. Coating thickness makes an even more important difference in the durability of colored finishes. Colors will fade more quickly with thinner coatings because they contain less of the coloring agent.
There is often enormous pressure to sell the “cheapest” product available. If a specification simply reads “Clear Anodized,” a 0.2 mil coating is the likely result. On the other hand, if a thickness of 0.8 mils is specified, the coating will last at least four times longer. Simply restated, the life of an anodic coating is proportional to its coating thickness, and a Class I coating is twice as thick as a Class II coating. This means that in most situations, Class I coatings will last twice as long a Class II on the exterior of a building.
As previously mentioned, anodizing can be renewed by cleaning. Anodizing can often be restored when it looks like it has failed, but when painted coatings fail, there is little that can be done short of repainting the entire building. Repainting a building is normally much more expensive than the cost of the original factory applied finish, and quality control is not good on a job site. Both anodized and painted coatings require regular maintenance, something most building owners do not consider.
The parts of a storefront which receive the most abrasion from traffic should be anodized. Anodizing’s superior abrasion resistance means it will outlast paint on a door stile, kick-plate or push/pull bar. On the other hand, painting aluminum framing materials above the doors adds a nice accent to a storefront. Sometimes, one will see aluminum doors installed in a mill finish to be painted at the job site. This is always a mistake. Even if a field applied PVDF coating is used, while the resulting finish might last longer than conventional paint, its abrasion resistance would still be lacking compared to factory-applied PVDF or anodizing.
Anodizing will probably always have a place in the storefront market. Its abrasion resistance and cost-effectiveness for storefront applications are not likely to be matched by any organic coating. Specify SAFINISH coatings for the most durable, long-lasting finish.
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The aluminum finish of choice depends on the application and is not merely a matter of personal preference. Anodizing is best suited to storefronts, and anywhere else a rich metallic appearance is desired. Anodized and Polyester coatings are best for storefront and handrails. PVDF coatings are best suited for metal roofing and curtainwall components. Anodized, PVDF and Polyester coatings could all be used on curtainwall, roofing and storefront applications with satisfactory results.
There are many options available for finishing aluminum, which is why it is such a popular construction material. The question of which finish to apply is not always an easy decision because of all the options available. I have tried to be objective to help the specifier decide what type of coating system to use when coating architectural aluminum, whether the application is metal roofing, storefront, or curtainwall. The conclusion I hope the reader draws from this article is to communicate your needs with your finisher or your finisher’s suppliers. With environmental regulations being the impetus behind many new developments, there will soon be even more options to the already vast array of finishes available for aluminum.
Kynar 500® is a registered trademark belonging to ARKEMA INC.
Hylar ® is a registered trademark of Solvay Specialty Polymers Inc.
-Penn McClatchey
http://www.glassmagazine.net/articles.php?id=806
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When embarking on a project that involves metal surfaces, selecting the ideal finish is crucial for the final product’s durability, appearance, and longevity. Two of the most popular finishes are anodized and powder coat, each offering unique benefits and drawbacks. But how do you determine which finish is best suited for your specific needs? This blog post will provide a comprehensive comparison of anodized vs powder coat finishes, guiding you in making an informed decision for your project.
Anodized aluminum...
Anodizing and powder coating are two distinct methods used to enhance and protect metal surfaces. Anodizing is an electrochemical process that forms a protective oxide layer on aluminum surfaces, while powder coating is a dry finishing process utilizing finely ground pigment and resin particles to create a protective layer on metal objects.
Each process offers unique advantages and disadvantages, which we will explore further in the following sections.
Anodizing is a surface treatment that increases the thickness and strength of the naturally formed oxide layer on metals like aluminum, providing enhanced resistance to wear, corrosion, and heat dissipation. The process involves immersing the aluminum surface in an electrolytic bath, which forms a protective aluminum oxide layer on the surface. Anodized coatings are popular across various industries due to their precise application and positive environmental impact.
Anodized aluminum is a popular choice for manufacturing industries. However, other metals such as bronze, gold, steel, etc., can also be anodized. This versatile process offers numerous benefits, making it an attractive choice for various applications.
Powder coating is a dry finishing process that applies a protective and decorative layer to various substrates. Here’s how it works:
The powder coating process offers numerous benefits, including a broad selection of colors and surface finishes, as well as reduced air pollution compared to liquid coatings due to the emission of no volatile organic compounds (VOCs). However, it is essential to have a proficient operator to achieve a high-quality powder coat.
Powder Coating...
To make an informed decision between anodized and powder coat finishes, it is crucial to compare their key features, such as durability, appearance, and environmental impact. Understanding the strengths and weaknesses of each process will help you determine which finish is most suitable for your specific project.
Anodizing is a process that creates a protective layer on the surface of metal. It is.
Anodized finishes offer superior durability and corrosion resistance compared to powder coat finishes. The benefits of anodized finishes include:
On the other hand, powder coating offers greater chemical resistance than anodizing. However, powder coatings can be more prone to chipping. The operating environment of the product should be taken into consideration when selecting between the two finishes for durability and corrosion resistance.
Anodized finishes have a lustrous, metallic look with limited color options. In contrast, powder coatings offer a wide range of colors and surface finishes, including matte, gloss, and textured. This makes powder coating an attractive choice for projects requiring vibrant colors or specific surface finishes.
It should be noted that with anodized finishes, any imperfections or tooling marks in the original piece will remain visible following anodization. Powder coatings, on the other hand, can effectively conceal any underlying material flaws, providing a more uniform and smooth appearance.
Anodizing can be eco-friendly with proper recycling and the use of alternative electrolytes, such as boric or phosphoric acid. Additionally, anodizing does not generate hazardous waste and is subject to regulations pertaining to wastewater discharges from metal finishing operations.
Powder coating is generally more environmentally friendly due to its low VOC emissions and simpler processes. The regulations governing powder coating involve the control of VOCs and hazardous air pollutants (HAPs). When selecting between anodized and powder coat finishes, it is essential to evaluate any environmental regulations and compliance that may be relevant to the project.
Both anodized and powder coat finishes are popular across various industries and applications. Understanding the typical uses for each finish will help you determine which process is best suited for your specific requirements.
Anodizing is a process that involves electrochemically treating the surface of a metal.
Anodized finishes, also known as anodized surfaces, are widely employed in building exteriors, appliances, food preparation equipment, sporting goods, and mechanical components due to their durability, corrosion resistance, and wear resistance. Additionally, anodized finishes offer superior adhesion for paint primers and glues compared to raw metal.
Their enhanced endurance and performance make anodized finishes ideal for heavy-duty applications, such as structural, architectural, and outdoor uses.
Powder coat finishes are commonly used for outdoor equipment, parts requiring vivid colors, and items needing durability and chemical resistance. They are widely used in the automotive industry and for coating metals in household appliances, aluminum extrusions, drum hardware, bicycle frames, guardrails, light poles, posts, signs, and fencing.
The flexibility of powder coat finishes makes them an attractive choice for a diverse range of projects, offering both protection and enhanced aesthetics.
When selecting between anodized and powder coat finishes, it is important to consider various factors that may influence your decision. Taking these factors into account will help you choose the most appropriate finish for your project.
Cost, durability, and aesthetics are all important considerations when deciding between anodized and powder coat.
Project budget and cost should be considered, as anodizing is generally more expensive than powder coating due to specialized equipment and materials, as well as the expertise and experience required for superior results. On the other hand, powder coating is typically more economical, making it a cost-effective solution for enhancing the aesthetics of metals that are not prone to rusting.
However, it is essential to have a proficient operator to achieve a high-quality powder coat, which may impact the overall cost of the project.
Desired aesthetics and surface quality play a significant role in the decision between anodized and powder coat finishes. Anodized finishes offer a luxurious, metallic appearance, while powder coatings provide a greater range of color options and can mask any irregularities in the base material.
Ultimately, the choice between anodized and powder coat finishes will depend on your project’s specific requirements, such as the desired look, feel, and performance of the final product.
Environmental regulations and compliance should be taken into account when selecting between anodized and powder coat finishes, as both processes have different environmental impacts and may be subject to specific regulations. Anodizing can be made more environmentally friendly with proper recycling and the use of alternative electrolytes, while powder coating is generally considered to be more eco-friendly due to its low VOC emissions and simpler processes.
Evaluating the environmental regulations and compliance related to both processes will ensure that your project adheres to any relevant guidelines and minimizes its environmental impact.
In conclusion, both anodized and powder coat finishes offer unique benefits and drawbacks, making them suitable for various applications and industries. Anodized finishes provide superior durability, corrosion resistance, and a metallic appearance, while powder coatings offer a wide range of colors, surface finishes, and greater chemical resistance.
By considering factors such as project budget, desired aesthetics, and environmental regulations, you can make an informed decision between anodized and powder coat finishes for your specific project. Ultimately, the right choice will depend on your unique requirements and priorities, ensuring a successful outcome that meets your expectations.
Anodized and powder coated finishes both offer superior protection to metal surfaces. Anodized coatings provide a deep, metallic finish that can create great aesthetic appeal.
Powder coating offers a wider variety of color options and provides better coverage of imperfections in the base material. Ultimately, it depends on the desired result, so it is best to research each option carefully.
No, anodizing and powder coating are not the same. Anodizing creates an oxide layer on a metal surface, while powder coating is a type of dry painting process that uses heat to fuse paint into a protective coating.
Although they both can be used to protect metal surfaces, the effects and application methods are different.
Anodizing can be a costly and time-consuming process, with setup and running costs that can be higher than other finishing methods. Additionally, the colors it produces may fade over time due to environmental factors like UV light exposure or extreme temperatures.
As such, anodizing can be an expensive investment with limited long-term results.
Powder coated windows are covered in a paint-like coating, while anodized windows have a protective oxide layer. The latter provides greater resistance to corrosive substances and wear, making it the superior choice for protecting metal window frames from the elements.
Anodized windows are more durable and require less maintenance than powder coated windows, making them the ideal choice for those looking for a long-term solution. They are also more resistant to fading and discoloration.
Yes, aluminum can be effectively powder coated with long lasting protection and attractive finishes. Powder coating is an environmentally friendly process that provides a tougher, more durable finish than standard wet paint. Making it ideal for use on aluminum surfaces.
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