Specifying Metal Coatings[August 2016]
Previously published in Metal Architecture - Read Here
As projects move from the design phase to construction, there comes the time when the products that will be used need to be specified. From the framing to the insulation, the metal panels to the skylights, specific products are chosen for each project. When it comes to deciding on the proper coating for the metal roof and wall panels, do you know what needs to be taken into consideration? We spoke to experts in the coil coating industry to find out everything you need to know when specifying metal coatings.
Kevin Ebert, vice president and general manager at Dura Coat Products Inc., Riverside, Calif., says architects are looking for an aesthetic value in the building that they're designing, and when it comes to coatings, they're looking for long-lasting beauty, and the best color and gloss retention. "There are minimum physical quality standards that [architects] want to meet relative to film thickness, a good color match, flexibility and hardness," he says. "All of the elements of a good, quality-controlled coating are important to architects."
Performance and Color Retention
Key to specifying metal coatings is determining the type of performance you are looking for. According to Jeff Alexander, vice president of North America coil and extrusions at Minneapolis-based Valspar Corp., you want to look for color performance in terms of chalk and fade.
Exposure to the sun, moisture and humidity, high temperatures and temperature fluctuations can all lead to color changes, chalking, blistering, corrosion and other physical factors to the metal coatings. Chalking is caused by degradation of the resin system at the finish's surface, and is usually due to exposure to ultraviolet (UV) rays. As resin breaks down, the resin particles take on a chalky appearance and imbedded pigment particles lose their adhesion to the film. Gloss is the coating's ability to reflect without any scattering of light. Direct UV exposure can degrade the topcoat luster. Fading is caused by UV and hydrolytic degradation of the resin system.
In addition to chalk and fade, Ebert says architects should be mindful of color and gloss retention, as well as adhesion properties. "You want a coating that's going to perform well during the life cycle of the building," he explains. "You also want it to continue to look good aesthetically with the color and gloss retention."
Tony Nicol, global segment manager, coil and extrusion at AkzoNobel Coatings Inc., Columbus, Ohio, says recommendations should be made based on what type of color retention an architect is looking for. Specifically, how well do you want the coating to stand up to the elements, and how much spark or pop do you want? Fluoropolymer coatings, such as polyvinylidene difluoride (PVDF), give better performance. "A PVDF coating will give the best color retention, the best resistance to chalking, and better gloss retention, which gives you an apparent color retention," he says. "If the gloss stays longer, then it looks like the color is holding its luster."
"The next highest quality is going to be silicon-modified polyester, or SMP," Nicol adds. "It's still going to give you excellent weathering characteristics, but it's just not quite as long lasting. However, it's got some additional benefits, such as having better impact resistance." Both are excellent products, he says, which will give excellent results.
To maximize performance of a coated substrate, Jerry T. Hatley Jr., executive vice president of CENTRIA Coating Services, Moon Township, Pa., says to take into account not just the topcoat, but the resin, pigmentation and primer technologies, the chemical pretreatment, as well as the specific metal substrate selection. "All of these elements build up a total system that maximizes the performance of the coated substrate," he says. "Your coil coating industry professional can provide a wealth of experience and assistance with developing an all-encompassing approach to materials specification."
There are three types of pigments used in architectural coatings: inorganic, organic and metalescent, also commonly known as pearlescent. Inorganic, which are generally ceramic or mixed-metal oxide pigments, are sourced from minerals that have been mined and refined such as red oxide, or have been synthesized at high temperatures, similar to firing ceramics. These colors generally belong to the earthtone family, while inorganic pigments tend to maintain their color for many years or decades.
Organic pigments, manufactured using petroleum-based (carbon) chemistry, can achieve bright, bold colors. However, their chemical structure tends to break down more quickly than their inorganic counterparts, and can be easily affected by sunlight, moisture and temperature changes. Composed of tiny metal flakes of aluminum, natural mica or synthetic mica-like material, metalescent pigments produce coatings that shine and sparkle as a result of the size and shape of the metal flakes. Depending on one's viewing angles and the light conditions, some coatings with metalescent pigments can change color.
According to Hatley, ceramic, or inorganic, pigments outperform organic pigmentation to a significant degree, and are vital to the overall performance of an exterior application. Nicol agrees, saying that while organics will give you bolder colors-reds, yellows, oranges and even blacks, ceramic or inorganic pigments will give you more consistent color for longer life. "The organic gives you a more pure color when you're looking at it," explains Nicol. "However, because they're organic, they break down more quickly. You're going to get a faster fade and you're going to lose that pop out of it."
Alexander notes that they've seen more vibrant pigment selections being made. "Architects are taking a cue from Europe and adding more color within their designs," he says. "One thing we're finding also, is that architects want custom colors on their projects, so their projects are different than everyone else's."
"The pigments of choice are cool, reflective pigments," Ebert says. "And the pigments that are selected are targeted to meet the minimum total solar reflectance values to make them Energy Star acceptable."
Another thing to consider when specifying metal coatings is where the project is located, says Scott W. Moffatt, architectural sales manager, industrial coatings, PPG Industries Inc., Pittsburgh. Is the project in a normal environment, an industrial environment, or even a coastal environment? Depending on where the project is located, the substrate used-aluminum or steel-or the coating system, can be different.
For example, Moffatt says a lot of people use aluminum on the coast, rather than steel based on corrosion concerns. "If we use steel and you're on the coast, we require thick-film primers," he explains. "So normal primers, which are applied at 0.2-0.3 mils, would require 0.8 mils on the coast with steel. And, sometimes in coastal and industrial environments, we'll apply clear coats to form another barrier and to help with staining from industrial fallouts."
Clear coats also will release salt residue easier than pigmented surfaces. Regular rainfall or maintenance schedules with fresh water rinsing will help increase the longevity of the building components. As a side note, Moffatt explains clear coats also enhance UV durability and premature chalk and fade. Chrome pretreatment and chrome primers are also essential ingredients to long life in a coastal atmosphere.
In normal environments, Moffatt says the standard is usually fine. But in industrial and coastal settings, extra steps are required to get the desired performance, especially since the paint will be exposed to different chemicals than in normal environments. "In coastal environments, there are four things that increase the formation of corrosion: heat, humidity, salt content and wind," he notes. "Those four elements are the worst conditions for corrosion and tend to be most severe in the Gulf States."
Color and Color Matching
Once you decide on which type of coating you're going to use, it's important to choose the right color. "You want to make sure you formulate the coating with a proven and durable pigmentation system," explains Moffatt. "You don't want it to prematurely fade, so it's very important to make sure the color, pigments and resins meet the performance standard you're looking for." Any weak link in the coating system could result in premature chalking or fading.
As Moffatt explains, most roofing is done in solid colors, without a metallic or mica flake. "Solids and micas don't require a clear coat to meet the performance required," he says. "You can apply a two-coat system-primer and top coat-and have a very durable coating system. If you use a metallic flake, a clear coat is mandatory. Without a clear coat to protect the metallic flake, the aluminum would tarnish and change from the original color requirement."
Specific coatings can also provide points for LEED certification. "With LEED, you have the heat island reduction-roof credit, which, when you use solar-reflective pigments, helps cool the building itself," explains Alexander. "It reflects the sunlight off the roof and keeps the building cooler, which helps with energy costs, with cooling the building, requiring less air conditioning, etc."
Coil coaters and paint manufacturers have labs to help achieve custom color matching. "A consultative approach to color selection yields accurate color matching, combined with the best possible specification of a long-life coating system designed to stand the test of time," explains Hatley. "Our passion for this business helps us collaborate with you to achieve color harmony with the surrounding environment, and with dissimilar exterior materials also."
Warranties by coating manufacturers are pretty comparable across the board. Most warranties cover film integrity, chalk and fade, and can differ depending on the coating technology and how many years you're looking for before replacement.
There are differences, however, in how the different companies stand behind their warranties. "The warranty is going to go through the fabricator and not directly to the coater," Nicol explains. "However, ultimately the fabricator is going back to the coating manufacturer. And, at the end of the day, the coating supplier is responsible for their piece of the warranty."