Steel is one of the most utilized materials in design and construction, owing to its durability, formability, and sustainability. Among its varied applications, pre-painted metal, also known as coil-coated or pre-coated metal, emerges as a staple choice for exterior finishes in residential, commercial, institutional, and industrial buildings. Used extensively for exterior wall cladding, metal roofing, trim, and accessories, pre-painted metal offers not only high quality but also aesthetic appeal. Its success hinges on three key factors:

1. The development of metallic coatings for steel substrates.
2. Advanced chemical pretreatments for all metal substrates.
3. Organic coatings that shield the metal from rust and corrosion.

These advancements have significantly propelled the growth of the metal building industry, empowering builders with limitless possibilities to actualize architectural visions.

As the popularity of pre-painted metal expands, builders often face the choice between pre-painted metal and pre-coated metals. While these options share similarities, a distinct difference lies in their purpose: paint primarily serves aesthetic ends, while coatings are engineered for performance.

Paint, enhancing the visual allure of metal, can be applied via various methods to a range of surfaces. However, its protective properties are secondary, leaving the substrate vulnerable to environmental factors. In contrast, coatings are meticulously formulated to safeguard the substrate against extreme weather conditions while preserving aesthetic appeal. When referring to pre-painted metal, it encompasses both coating and painting processes.

The evolution of coating and paint formulations bolsters protection and broadens design options, spanning an array of colors and textures. Coatings, when factory-applied, offer superior consistency, durability, and eco-friendliness compared to alternatives. Other advantages include enhanced mechanical strength, corrosion resistance, and a robust substrate supporting advanced paint applications.

In this course, we delve deeper into the multifaceted traits of pre-painted coiled metal, exploring its creation, design, and performance aspects. Moreover, we shed light on its sustainable characteristics and offer insights into selecting metal building components.

PRE-PAINTED METAL OVERVIEW

Metals, produced in mills, serve as raw materials for a myriad of products. While structural steel members undergo forging processes to attain desired shapes for buildings and structures, mills yield metal coils through heating and rolling. The thickness of the metal, or gauge, determines the profiles rolled from the coil, making it adaptable for various applications. Post-forming processes, particularly cold-forming, shape coiled sheet steel into metal components like studs, girts, purlins, wall panels, roof panels, trim, and accessories. Cold-formed bending augments structural strength by introducing corrugations, enhancing stiffness.

Material Options

Steel and aluminum are two primary substrate choices for pre-painted metal in buildings. Steel, valued for its economic efficiency and engineered performance, boasts yield strengths ranging from 40,000 to 80,000 psi. Conversely, aluminum, lighter in weight with lower yield strengths of 18,000–30,000 psi, offers ease of formability. Both metals integrate high recycled content and ensure full recyclability at the end of their service lives. The pivotal distinction lies in their corrosion resistance, with steel requiring protective coatings against rust and aluminum forming a natural oxide layer for inherent corrosion resistance.

Coating Process

Although hot-dipped steel or aluminum can be installed without coating, it is customary, especially for exterior applications, to apply a protective coating. Pre-painting in a controlled factory setting is the most cost-effective, durable, and reliable method, akin to automobile paint application. This pre-applied coating shields the metal from weather elements and ensures design consistency across the building, facilitating flexibility in finish options.

The coating process commences at a coil-coating facility, where coils of steel or aluminum undergo unrolling, cleaning, chemical conversion coating, priming, and top-coating. Speeds of up to 700 feet per minute are achieved, resulting in high output with unparalleled precision and environmental friendliness compared to alternative painting methods.

Cost Factors of Pre-Painted Metal

Despite common misperceptions regarding its affordability, pre-painted metal offers great economic value over the long term. Analyses affirm its extended lifespan, minimal maintenance requirements, and positive impact on building appearance, thus enhancing the overall return on investment. Manufacturers of metal buildings typically provide complete building packages, including framing and cladding, further optimizing project ROI.

Design Aspects of Pre-Painted Metal

Pre-painted metal’s aesthetic versatility is exemplified in new or renovated buildings requiring architectural metal walls and roof panels. From a diverse palette of colors to special effects, such as mica/metallic shimmer and varied gloss levels, pre-painted metal offers boundless design possibilities. Whether stamped-in or embossed, texture adds depth and visual interest, contributing to a building’s overall aesthetic appeal.

Pre-painted metal walls and roof panels serve as significant design elements across diverse building types, offering refined exteriors and opportunities for differentiation and branding. This design flexibility extends to retrofitting existing buildings, offering a cost-effective means to revitalize aesthetics, improve durability, and enhance energy performance and sustainability.

PERFORMANCE CHARACTERISTICS OF PRE-PAINTED METAL

You may ask yourself, “What contributes to the excellent performance of pre-painted metal?” Beyond the core of treated metal, the performance of pre-painted metal comes down to enhancements and formulations of the coating. Just as custom finishes and coloring are perfectly combined to create the desired outcome, it is possible to customize coating formulation to create heightened characteristics.

The National Coil Coating Association (NCCA), an established trade organization dedicated to the growth of coil-coated products, has developed a series of technical manuals referred to as “Toolkits” (www.coilcoating.org/toolkits) that discuss metal panel performance. Specifically, Toolkit #26 focuses on the long-term performance of metal building panels and buildings. It notes three principal factors 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.

• Pigment performance: While the resin choice (PVDF, SMP, or polyester) is the single most significant determinant of overall performance, all coil coatings are baked at temperatures much higher than those of other industrial coatings. This means that coil-coating topcoats, including the pigments selected, must provide heat resistance and high-tolerance qualities. Once the finished products are installed on buildings, the pigments should provide exceptional weathering performance properties for 20–40 years or longer. These performance properties include resistance to chalking and fading of the pigment colors, corrosion resistance (particularly in primer systems), chemical resistance, resistance to degradation from ultraviolet radiation, the reflectivity of solar radiation, and more.
• Environmental performance: Different project locations bring different environmental conditions that warrant a specific coating type. In addition to this, special attention must be paid to the selection of the base metal and pre-treatments. For example, some products may be placed in remote locations with aggressive UV light conditions, corrosive salt spray, or higher-than-typical temperature exposure. Others may be in industrial locations with the presence of chemicals. Selecting the correct metals and coatings can address these environmental conditions. Another example is smog, often in urban or heavily populated locations. In this instance, choosing a specialized coating with smog-eating properties would be useful. Pre-painted steel that limits adhesion or penetration can be selected in places prone to graffiti, making graffiti removal much easier than with other materials.
• Water performance: Materials used on building exteriors will encounter water in the form of rain, sleet, melting snow, ice, or other weather-related conditions. Pre-painted metal products remain clean because metal inherently sheds water better than other materials.

Overall, virtually every geographic location and project type can benefit from pre-painted metal performance. In the western United States, lightweight metal roofing and wall panels reduce seismic mass and offer non-combustible, high-temperature resistance in the case of wildfires. In the storm-prone southern United States, pre-painted metal products are highly resistant to uplift from hurricane winds. In regions with high humidity, like the eastern United States, mold does not grow on metal. The substrate metal and coating process determine how resistant the metal material is to rust or decay. In the Midwest, where hail is often a concern, resistance to hailstorms 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 the most optimal solution.

GREEN BUILDING CONTRIBUTIONS OF PRE-PAINTED METAL

Pre-painted metal manufacturers have contributed significantly to developing products that support the green and sustainable nature of buildings. In fact, many manufacturers have helped architects and designers achieve certification under the LEED program, ENERGY STAR programs, and the Living Building Challenge, among others. Some of the ways in which they have been able to do this include the following:

• Cool roofing: Several national programs recognize the significance of keeping roof temperatures cool. These programs also provide ways to measure and document the relative heat or coolness of different types of roofing. Some highly recognized programs include the ENERGY STAR Roofing Products Labeling program (energystar.gov) and the Cool Roof Ratings Council (CRRC). Pre-painted metal roofs have been tested under these programs and shown to provide significant solar infrared reflectance and thermal emittance, both of which can reduce the surface temperature of a roof. This is achieved mainly through solar-reflective (SR) pigments in the coating. These roofs reflect heat emitted by the sun back into the atmosphere. This lowers the roof’s temperature and reduces the heat transferred into the building, decreasing energy consumption.
• Energy performance: Cool roofing reduces the creation of “heat islands,” which have been shown to increase ambient outdoor air temperatures noticeably compared to green or more natural areas. It also reduces the cooling load of a building by reflecting away the heat, which results in less energy usage due to less frequent air-conditioning runs.
• 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. This substitution will eliminate costs and avoid the complications of reroofing with a solar array in place. The various attributes related to energy help protect the natural environment by reducing the air pollution caused by the demand placed on power generation plants. They also lower the local air temperature in urban areas, which in turn helps minimize smog formation.
• Materials and resources: Pre-painted metal products generally have a routine life-cycle assessment, which evaluates their environmental impact, health impact, and end-of-service-life options. These assessments result in a favorable outcome because metal wall and roofing products demonstrate significant longevity compared to products made of a different material. For example, it is common for metal roofing to last 50 to 60 years or longer, while other roofing would last only one-third to one-half as long.
• Material transparency: Manufacturers have made great strides in avoiding harmful elements and ingredients. For example, pre-painted products have significantly reduced usage of Chromium 6 content. This helps make them compliant with the Living Building Challenge Red List requirements.
• Recycled content: A significant green aspect of metal is that a high percentage of pre-painted metal is made of recycled content. This makes recycling at the end of its lifecycle very easy and noteworthy.
• VOC reduction: Historically, volatile organic compounds (VOCs) played a prominent role in the coating industry because they contain properties that assist in applying coatings to a surface. However, their use has been dramatically reduced since VOCs are recognized as contributing to the generation of ground-level ozone, urban smog, adverse health effects, and environmental issues. Modern coil-coating processes incorporate a thermal oxidizer that destroys the VOC gases released during the coating process and prevents them from entering the atmosphere to mitigate the harmful effects of VOCs. The energy generated during this process is returned to the facility in the form of heat, where it can be used to preheat fresh air entering the baking ovens or to heat part of the facility. This results in more environmentally friendly products, even before they leave production. Once the pre-painted metal products are shipped, there is no need for on-site paints or coatings, so no other VOCs should need to be introduced.

In general, there are multiple ways that pre-painted metal products currently contribute to green and sustainable buildings. New and innovative initiatives are also being developed every day. 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 dust, which can be washed off the surface and remain clean. We are sure that more innovative solutions will be introduced in the realm of sustainability.

SPECIFYING PRE-PAINTED METAL PRODUCTS

When specifying pre-painted metal products, there are numerous choices and options from which to select. Coordination with manufacturers during the design phases of a project will help gain insight into project-specific details, cost drivers, installation nuances, and all the latest options. In a standard CSI or MasterFormat, the typical locations for specifying coil products are 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, MBMA publishes a Metal Building Systems Manual with a Performance Guide Specification. This guide specification is a free download at www.mbma.com and an excellent resource for specifying all metal building products. Some relevant items to address in a standard three-part specification format are highlighted below.

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

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 code-specific requirements for exterior walls and roofing. This includes requirements for fire ratings, wind, and weather resistance. Regarding 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.

Pre-painted metal product submissions should include the manufacturer’s data and information for all specified products, including color/finish samples. This information will be used to confirm that the appearance is acceptable and meets the aesthetic and performance requirements of the project.

Quality assurance is a significant part of any field-installed system. Installers are required to meet the qualifications set by the manufacturer of the metal products. Approved installers should provide the required documentation to the appropriate project chain of command as outlined in the specifications. Field professionals should also meet or exceed the minimum qualification requirements to ensure the installation is 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.

Part 2: Products

All pre-painted metal products specified should be defined in the record documentation, including the component type, substrate, thickness/gauge, coating type, formulation, and color. If multiple products are used, they should each be identified by type in the specifications. Additionally, the locations of each building component need to be called out in either the drawings or specifications. The details of the specified products can include:

The base metal of the products needs to be called out (steel or aluminum), including the type of pre-treatment (galvanized, galvalume, etc.).

Each metal product or panel’s thickness (gauge) needs to be identified.

All wall and roof panel types need to be identified and specified fully.

The type of coating based on resin type (PVDF, SMP, or polyester) needs to be identified for each product.

The formulation requirements or specific formulation preferences for the coatings need to be identified (i.e., primers, color coats, mica/metallics, performance additives, gloss/sheen, etc.)

All colors, textures, and other finish characteristics need to be identified for each product. The manufacturer’s literature should always be referenced.

In addition, all trim, accessories, and related items need to be identified in the specifications, ideally as part of a complete, coordinated system.

Part 3: Execution

As with any site-installed product, the installation requires multiple steps to be clearly articulated in the specification to achieve the best results.

• Examination and preparation: The importance of this step should always be stressed. In addition to the architect, the installer should review and examine the substrate for conditions affecting the performance of roofing or siding. Ultimately, the goal is to provide a substrate surface prepared to an acceptable level, clean of all contaminants, and free of any debris.
• Installation: Engineering and manufacturer’s instructions should be followed here for a properly coordinated, successful project.
• Protection: Once applied, most pre-painted metal products are ready to go. However, if unusual conditions are expected during the remainder of construction, they should be protected accordingly.
• Cleaning: Upon completion, the finished surfaces should be cleaned of any construction or miscellaneous dirt, debris, etc., using soft, damp cloths.

When specified and installed correctly, pre-painted coiled metal will provide the desired look and long-term performance characteristics that are intended.

There are many design and performance considerations when selecting products for the exterior of buildings. Pre-painted metal products, including metal roofing and wall panels, are a popular and sustainable choice worth considering. Metal roof and wall panels are applicable for a full range of building types and are suitable for new construction and renovation projects. Suppose you need a versatile, durable, sustainable solution for your building. In that case, pre-painted metal products are a viable option that is easy to maintain and has a proven track record of longevity.