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Continuing Education
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After reading this article, you will be able to:
Steel and aluminum are used extensively in design and construction because they are durable, formable, and sustainable metals. In particular, pre-painted metal, also referred to as coil-coated metal or precoated metal, is commonly used on the exterior of all types of residential, commercial, institutional, and industrial buildings, both as exterior wall cladding and for metal roofing including related trim and accessories. Part of the reason for its ongoing success and growth is the development of metallic coatings for steel substrates, as well as advanced chemical pretreatments for all metal substrates, along with organic coatings that protect the metal from rust and corrosion. Relatedly, these advances in pre-painted metal roof and wall panels have contributed significantly to the growth of the metal building industry and provided unlimited options to create virtually any architectural vision.
Photo courtesy of National Coil Coating Association (NCCA) Pre-painted metal products are commonly used on building facades and roofing to create economical, sustainable, and well-designed buildings that perform extremely well over the long term. A distinction needs to be made between paints and coatings since there is a difference. Simply put, paint is for aesthetics, and a coating is for performance. Paint can be applied to a variety of surfaces using many different application methods. While there are some protective qualities that come with painting, this is not the real purpose of paint (e.g., drywall can still be damaged by water, etc.). Coatings are formulated specifically to protect the substrate and withstand, in this case, extreme weather conditions and maintain the aesthetic beauty of the metal building products. Pre-painted metal in this course will refer, nonetheless, to metal that has been both coated and painted.
The advancement of coating and painting formulations offers not only protection but also a wide variety of design options that include a full range of color and texture possibilities. Further, when the coating is factory applied, it is more consistent, durable, and environmentally friendly than other alternatives. The appeal of pre-painted metal includes mechanical strength, corrosion resistance, and an excellent base substrate upon which to apply advanced paints. Based on all of these factors, this course looks more closely at the multiple traits of pre-painted coiled metal. Specifically, it delves into the process of creating pre-painted metal, the design and performance aspects that can result, the green and sustainable characteristics of the products, and some insights into selecting and specifying durable, attractive, and sustainable metal building components.
Metals are produced in mills into a variety of products. Structural steel members, for example, are formed using heat and traditional forging processes into sizes and shapes suitable for buildings, bridges, and other structures. The weight and dimensional area of these shapes typically determine the inherent strength of these products. By comparison, mills also produce coils of metal in a different process involving heating and rolling of the metal into a continuous ribbon that is coiled up onto a roller. In these cases, it is the thickness (i.e., gauge) of the metal that determines the profiles that can be rolled most effectively from the coil, making it suitable for a variety of subsequent uses. While its width is determined by the milling process, individual sheets of steel can then be cut to length before, during, or after a post-forming process at a separate fabricating facility. The most common post-forming process of the coiled sheet steel is that of cold-forming (i.e., no significant added heat, just a series of rollers to shape the steel as it passes through). This is used to turn flat, coiled sheet steel into metal shapes, such as creating cold-formed metal studs, metal girts and purlins, metal wall panels, metal roof panels, metal trim, or metal accessories. This cold-formed bending and shaping of the metal can also add strength through the creation of structural “L” or “U” shapes or simply by adding rounded or squared corrugations to the flat metal, thus adding stiffness.
There are two fundamental substrate choices for pre-painted metal in buildings: steel and aluminum. Steel is generally found to be the more economical option for many building products and has become a highly engineered material for both performance and appearance. Steel is known for its strength, even in coiled or sheet products with yield strengths ranging from 40,000 to 80,000 pounds per square inch (psi). Aluminum, by comparison, is lighter in weight than steel but does have a very high strength-to-weight ratio. Compared to steel, though, aluminum has generally lower yield strengths on the order of 18,000–30,000 psi, meaning it is a somewhat softer material and easier to form. Both metals are quite commonly used nonetheless and typically incorporate high amounts of recycled content—with full recyclability possible at the end of their service lives.
The primary difference between the two metals is their ability to resist corrosion. Untreated steel will interact with air and water and eventually rust and corrode. Aluminum does not react the same way. When exposed to the environment, it quickly forms a microscopically thin aluminum oxide layer, which provides inherent corrosion resistance. To create such a protective layer on steel, it is routinely coated by a hot-dip coating method with other specific metals to assure its integrity over the long term. There are three common metallic coatings that rely on hot-dipping steel sheet into a bath of molten zinc or a zinc/aluminum alloy as follows.
Because of aluminum’s inherent corrosion resistance, it does not require metallic coatings as described above for steel.
Image courtesy of the National Coil Coating Association (NCCA) Pre-painted coil-coated metal consists of a base metal material that is coated on both sides with primer and finish coats or backers. Hot-dipped steel or aluminum can be installed without a coating, but this is not the common approach, particularly for exterior applications. Instead, a coating is commonly applied to the metal. The most cost-effective, durable, and reliable way to do this is to pre-paint the metal in a controlled factory setting. This allows for the paint and coating to be “cured” using heat much the same way that automobile paint is applied for a long-lasting, durable finish. This pre-applied coating does two things. First, it provides a fundamental level of protection to the metal against weather, sun, and other elements. Second, it allows for a wide range of design flexibility by selecting one or more finish options (color, texture, etc.) for the metal that is consistent with the design intent of the building.
The process of applying the coating begins with a coil-coating facility that receives coils of steel or aluminum in the desired size and thickness/gauge. The coil(s) are placed into a processing sequence where the metal is first unrolled, accumulated, and readied for further processing. Both sides of the core metal are then cleaned and receive a chemical conversion coating. When the metal is dried, it is then primed on both sides by passing through a coater and a curing oven. When ready, it continues on to a finish coater—the exposed side receiving a finish top coat, and the concealed side receiving a backer coat. Typically, the primer and finish coats of the exposed side of the metal are thicker than the coats of the concealed side of the metal.
Image courtesy of the National Coil Coating Association (NCCA) Pre-painted coil coating is a process that is fast, tightly controlled, and environmentally friendly. It is worth noting the rate at which coiled metal is processed (i.e., cleaned, pretreated, primed, and top-coated) on a typical coil-coating line. The metal strip is processed at speeds up to 700 feet per minute, and the strip itself is usually about 4 feet wide. This means a metal strip 4 feet wide being processed at a rate of 700 feet per minute produces 2,800 square feet of coated metal per minute. Of course, not all coating lines operate at this maximum speed, so a more typical output may be 1,500–2,500 square feet per minute. Most other application processes (such as spray painting) require at least 10 times longer to equal the area coated by the coil-coating process. In fact, no other painting process is as fast, tightly controlled, and environmentally friendly as the coil-coating process.
What is in a coating? Coatings manufacturers have developed many different formulas that are used to protect metal building components. Since the coating technology has been around for many years and many individual contributions have been made to its advancement, there are a lot of attributes that can be readily achieved. The key is to pick the proper coating for the intended use—not all coating formulations or types of products are the same. While each coating formula has its own unique benefits and intended use, the majority of the formulas use a mixture of four primary ingredients: pigments, resins, solvents, and additives.
Here is how each of these ingredients fills a role to create the most effective coating.
Image courtesy of the National Coil Coating Association (NCCA) The ingredients in a coating typically include 15 percent pigments, 35 percent resins, 50 percent solvents, and 1 percent additives. The resin is arguably the most important ingredient in the coating system because it determines the overall performance of the coating. As such, coatings are generally described by using the name of the type of resin used. There are three primary resin-based coating systems used for finishing sheet metal. Each is discussed as follows.
Pre-painted steel using the appropriate coating finish provides a durable and appealing material that can then be shipped to a metal building manufacturer or metal component fabricator to create the final architectural products. PVDF and SMP coatings in particular are durable and flexible enough to withstand the cold-forming processes and perform well once in place on a building project. For more information comparing the properties and performance of the three primary resin-based coating systems, see NCCA Toolkit #8, “Coil Coating Topcoat Systems,” Appendix A (www.coilcoating.org/toolkits).
There can be a misperception that pre-painted metal is simply too expensive for many buildings. The reality is that many building owners can indeed afford to use these products. This is because life-cycle cost analyses prove them to provide great economic benefit. They commonly last longer and do not need replacing as often as other materials do. They also require little to low maintenance, saving on those costs every year that the material is in place. Since pre-painted coil metal is used for very visible parts of a building, such as exterior wall cladding or metal roofing, the positive long-term appearance can help building owners portray the best image of their enterprise, thus boosting revenue. In the case of metal buildings, most manufacturers produce their own roll-formed steel roof and wall panels. By providing a complete building package, including building framing and cladding, they improve the ROI for the entire project.
The visual aspects of pre-painted metal, particularly when used for architectural metal wall and roof panels on new or renovated buildings, are diverse and versatile. This comes from a combination of the features of the panels that are fabricated from pre-painted coil stock and the color(s) or special effect selected.
The first fundamental design choice when using metal panels for wall, roofing, or other metal building components is the desired profile. This is the cross-sectional shape of the panels that gives it the three-dimensional texture or form on a building.
First, when considering metal wall panels, there are several profile options:
For more information, please visit jinhu. Photo courtesy of the Metal Building Manufacturers Association (MBMA) Metal roofing and wall panels are available in a wide range of profiles and appearances. Second, metal roofing panels also offer a range of different profile options, including the following.
In addition, to selecting the right profile for a metal wall or roof panel for a project, the visual, aesthetic aspects of the surfaces are clearly important. Since we navigate our environment with our eyes, 80 percent of the information about our world comes from our visual sense. Hence, the following aspects can all play a significant role in the aesthetic design.
Image courtesy of the National Coil Coating Association (NCCA) The color of pre-painted coil-coated metal and some of the characteristics of that color are determined by the mix of pigments that are used, including choices from organic or inorganic pigments, or both. Images courtesy of the National Coil Coating Association (NCCA) The texture of either the metal substrate or the paint coating can be enhanced to suit individual project conditions. By paying attention to all of the above factors and options, pre-painted metal wall and roof panels can be used as significant design elements for all types of buildings. In some cases, it might simply be the opportunity to create a refined and elegant exterior design solution. For others, it can provide differentiation from adjacent buildings or even provide branding opportunities for the owners. This is common with retail, hospitality, and restaurant companies that seek a strong, consistent look for their buildings in multiple locations. Pre-painted metal assures a consistent appearance and design quality regardless of location.
Keep in mind that all of these benefits are not just for new buildings. Existing buildings can be retrofitted with pre-painted metal panels as a dramatic and cost-effective way to create a totally new appearance or enhance an existing style and aesthetic. In the process, the metal components can improve the durability and longevity of the building and help bring the building more up-to-date on energy performance and sustainability.
What contributes to the excellent performance of pre-painted metal? Beyond the core of treated metal, it comes down to enhancements and formulations of the coating. Just as custom finishes and coloring are possible, so too can the performance characteristics be customized and worked into a coating formulation. There are also industry guides developed by the National Coil Coating Association (NCCA), which is an established trade organization dedicated to the growth of coil-coated products. NCCA has developed a series of technical manuals referred to as “Toolkits” (www.coilcoating.org/toolkits). Specifically, Toolkit #26 focuses on the long-term performance of metal building panels and metal buildings. It notes that there are three principal factors that influence that performance: 1) the choice of materials, 2) the environment in which the products are placed, and 3) the variability of coating processes. By following the guidance contained in these documents, manufacturers can achieve consistent, high-quality results, and specifiers can identify acceptable tolerances and performance parameters.
Overall, virtually every geographic location and project type can benefit from some aspect of pre-painted metal performance. In the western United States, lightweight metal roofing and wall panels reduce seismic mass and offer noncombustible, high temperature resistance in the case of wild fires. In the storm-prone southern United States, pre-painted metal products are extremely resistant to uplift from hurricane winds. In the humid eastern United States and elsewhere, mold growth is not supported on metal, while resistance to rust or decay from water is based on the choice of substrate metal and coating process. In the Midwest, where hail is often a concern, resistance to hail storms can be factored into the strength of the metal as well as the durability of the coating. In short, regardless of the conditions or locations, pre-painted metal has been successfully used to create an appropriate solution.
Like most other building components, pre-painted metal manufacturers have developed products that can contribute to the green and sustainable nature of buildings. Indeed, many have helped building designs achieve certification under the LEED program, ENERGY STAR programs, and the Living Building Challenge, among others. Some of the ways they do that include the following:
Photo courtesy of the Metal Building Manufacturers Association (MBMA) Cool metal roofs have been shown to be a very energy-efficient and cost-effective strategy to contribute to green and sustainable buildings. Standing-seam metal roofing panels provide an ideal substrate for installing electricity generating solar panels (i.e., photovoltaic or PV panels). Solar pre-painted panels can be easily attached to the upright standing seams using non-penetrating clamps. Further, the long life of a metal roof will outlast the life of the solar panels, thus eliminating costs and complications of reroofing with a solar array in place. All of these energy-related attributes help the natural environment by reducing the air pollution caused by the demand placed on power generation plants and lowering the local air temperature in urban areas, which helps to minimize the formation of smog.
In general, there are multiple ways that pre-painted metal products currently contribute to green and sustainable buildings. There are also new and innovative initiatives being developed. One intriguing technology is the use of coil coatings that can react with pollutants in the air surrounding it. The chemical reaction creates a harmless transformation into water vapor, inert gas, and some dust that can be washed off of the surface and remain clean. Stay tuned, as there is more to watch for on the sustainability front.
When specifying pre-painted metal products, there are clearly numerous choices and options from which to select. Coordination with manufacturers during the design phases of a project will help gain insight for project specific details, cost drivers, installation nuances, and the latest options. In a standard CSI or MasterFormat, the typical locations when specifying coil products is in Division 5: Metals and Division 7: Thermal and Moisture Protection. The subsections are 05 05 10 (Factory-Applied Metal Coatings) and 07 40 00 (Metal Roofing and Siding). Alternatively, the products could be part of a complete Metal Building System specified in Special Construction Section 13 34 19. In this case, note that MBMA publishes a Metal Building Systems Manual that includes a Performance Guide Specification. This guide specification is a free download at www.mbma.com and is an excellent resource for specifying all types of metal building products.
Some of the relevant items to address in a standard three-part specification format are highlighted as follows.
Metal building products and coatings are designed to meet the applicable building codes (i.e., IBC) and energy codes (i.e., IECC, ASHRAE 90.1.), including all of the code-specific requirements for exterior walls and roofing. This includes requirements for fire ratings, wind, and weather resistance. In regard to the paint systems and coatings, standards are referenced for compliance and performance. Certifications are available from UL based on various ASTM standards for coating performance. There are also guidelines from the Fenestration and Glazing Industry Alliance (FGIA), a merger between the American Architectural Manufacturing Association (AAMA) and the Insulating Glass Manufacturers Alliance (IGMA), effective January 1, 2020, including AAMA 621: Voluntary Specifications for High Performance Organic Coatings on Coil Coated Architectural Hot Dipped Galvanized (HDG) and Zinc-Aluminum Coated Steel Substrates.
The scope of specification work can include all preparation work, substrate review, product choices, and final installation. In terms of specifying performance, the appropriate testing standards should be referenced. (See sidebar.) Submittals for pre-painted metal products should include manufacturer’s data and information for all specified products, including color/finish samples to confirm that the appearance is acceptable and meets the aesthetic and performance requirements of the project.
Quality assurance is clearly an important part of any field-installed system, and the same is true here. Installers should have qualifications acceptable to the manufacturer of the metal products. Approved installers should provide required documentation to the appropriate project chain of command as outlined in the specifications. Field professionals should meet or exceed the minimum qualification requirements as defined to ensure that the installation will be performed successfully.
On-site protection of products should be carried out according to the manufacturer’s instructions and recommendations. Similarly, the manufacturer’s standard limited warranty for wear, defect, bond, and conductivity can be requested and sought for the entire installation.
All pre-painted metal products specified should be defined in the record documentation, including type of component, substrate, thickness/gauge, coating type, formulation, and color. If multiple products are used, they should each be identified by type in the specifications, and the locations of each building component need to be clearly called out in either the drawings or specifications. The details of the specified products can include:
In addition, all trim, accessories, and related items need to be identified in the specifications, ideally as part of a complete, coordinated system.
As with any site-installed product, the installation requires multiple steps that need to be clearly articulated in the specification to achieve the best results.
When specified and installed correctly, pre-painted coiled metal will provide the desired look and long-term performance characteristics that are intended.
When it comes to selecting products for the exterior of buildings, there are many considerations to take into account, both in terms of design and performance. Pre-painted metal products, including metal roofing and wall panels, are clearly a popular choice worth considering for a full range building types. They are quite suitable for both new construction and renovation projects. Specifying pre-painted metal products is a versatile, proven, long-lasting, durable, sustainable, and easy-to-maintain solution. If you are looking for more details, kindly visit Painted Aluminum Coil For Roof Tiles.
PRE-PAINTED METAL OVERVIEW
Material Options
Coating Process
Coating Options
Cost Factors of Pre-Painted Metal
DESIGN ASPECTS OF PRE-PAINTED METAL
Metal Panel Profiles
Pre-Painted Metal Aesthetics
PERFORMANCE CHARACTERISTICS OF PRE-PAINTED METAL
What contributes to the excellent performance of pre-painted metal? Beyond the core of treated metal, it comes down to enhancements and formulations of the coating. Just as custom finishes and coloring are possible, so too can the performance characteristics be customized and worked into a coating formulation.
GREEN BUILDING CONTRIBUTIONS OF PRE-PAINTED METAL
SPECIFYING PRE-PAINTED METAL PRODUCTS
Part 1: General
The scope of specification work can include all preparation work, substrate review, product choices, and final installation. In terms of specifying performance, the appropriate testing standards should be referenced. (See sidebar.)
TESTING STANDARDS AND SPECIFICATIONS
Part 2: Products
Part 3: Execution
CONCLUSION