How Architects Can Specify the Right Metal Finish – Part 1
Painted Metal is an amazing product – its finish offers unmatched durability, flexibility, and color vibrancy to suit any project’s needs. However, in today’s market, product specifiers are swamped with a vast array of color and finish options. Contrasting terminology amongst manufacturers, differing warranty provisions, and varying levels of manufacturer sophistication, contribute to the complexity in the finish selection process. Inappropriate finish selection, digital representation limitations, and improper field installation practices can also translate to design visions mismatching with end solution reality. To help demystify the different elements of a painted metal finish, to encourage specifiers to select an appropriate color and finish, and to ensure design vision is translated into reality, Steelscape has created this four-part series on specifying a painted metal finish. Overall, we hope this summary provides architects with the tools needed to feel more comfortable and confident when specifying metal roofing and metal siding in their designs.
Understanding the Constructs of a Metal Finish – Part 1
A broad range of products exists in today’s market for exterior roof and wall surfaces. Material selection is often based on project budget, design vision, product performance, and durability. Metal is an emerging popular exterior cladding material as it’s able to satisfy a broad scope of project considerations and still provide creative flexibility. This creative flexibility fosters innovation and the movement toward creating complete, cohesive urban designs through mixed-use building materials with metal as its foundation.
Creativity and logic meet to create engaging metal designs that meet end-user needs. Metal is a prevalent building material utilized in school, multi-family, civic building, and custom home designs. This is due in part where creative vision must meet the needs of stringent budgets, long structural life spans, and demanding building user acceptance criteria. The Elk Grove Animal Shelter in Northern California is a case in point. They selected a combination of metal siding and roofing in conjunction with wood and stone materials to create a memorable, warm environment for both people and animals alike. Lead architect, Eric Wohle, noted that metal siding, roof, and soffits were chosen to add visual interest, durability, and cost-effectiveness from both an environmental and capital cost perspective.
What sets metal apart? Unlike many other finishes, the final painted layer of metal is applied before it’s formed into a finished product, such as a standing seam roof or corrugated wall panel. This is significant as it means the paint is applied in a contained, controlled environment enabling uniform thicknesses with high finish consistency and quality. Most pre-painted metal undergoes up to 10 separate test protocols to ensure quality specifications are met. These specifications include color, cure, adhesion, and corrosion resistance resulting in a surface finish that is exceptionally durable. As the paint is applied prior to forming into a finished product, this also means that the paint is exceptionally durable as it must withstand the forming process yet still offer a final finish warranty of 30 years or more. This paint application method is environmentally responsible as it is applied in a closed-loop system. Volatile Organic Compounds (VOCs) created in the painting process, whereby liquids converted to a solid, are burnt and used as fuel rather than released into the atmosphere. The flexibility created by painting on a dedicated paint line before being formed into a finished product further expands the array of colors and finishes available to the design community.
Painted Metal Finish Contributes to Durability
There are several layers to a painted metal finish that contribute to its durable surface.
The product core is metal, usually comprised of steel, for the combination of strength, affordability, and weight. Steel material thickness is called gauge and is a driver of product strength and price which impacts key performance metrics such as profiles design loading values and wind performance values. The material thickness also impacts how easily a panel is formed into shapes and its propensity for oil-canning. Oil-canning is a visual phenomenon seen as waviness or distortions in flat surfaces of metal roof and metal siding products. Stresses in the base material, improper fastener pressure, misaligned panels, and thermal expansion can contribute to oil-canning. Roof products with striations, a minor raised accent lines, and a heavier gauge material may reduce these effects.
Steel is enclosed on both sides with a metallic coating that usually consists of zinc (Galvanized) or aluminum-zinc (Galvalume® or ZINCALUME®) to provide enhanced corrosion protection. Corrosion is the electrochemical reaction between the metal and its environment resulting in thinner and weaker material over time. The metallic coating serves to slow the rate of corrosion and is a critical layer for product longevity. Aluminum-zinc (Galvalume®) metallic coated panels have a proven lifespan of 60-years or more in the field. Paint is then applied to the product. While the top layers are important, products don’t necessarily need to be painted. Aluminum-zinc metallic-coated steel is commonly sold bare with a thin resin coating to make it easier to form. These products typically have a silver-metallic aesthetic once installed that will dull over time yet still offer exceptional durability.
If the product is painted, prior to painting the metallic-coated steel is applied, pre-treatment to clean the surface is important in preparing it for optimum paint adhesion. The painted layer of a metal product will consist of two key layers, the primer and the topcoat, with some paint systems offering an optional clear coat for certain applications. These layers must be designed to interact and adhere together which is why these layers are referred to as the paint system.
Primers provide ‘bite’ for paint adhesion and directly support topcoat color, flexibility, and provide corrosion resistance. In severely corrosive environments, high build primers can be used to provide additional protection and warranty coverage. The topcoat layer protects from the outside elements and provides color and aesthetic appeal. The durability and weatherability of the topcoat reflect its resistance to moisture, sunlight, and temperature changes.
For some paint systems, a clear coat is applied over the top, which can serve three purposes.
- Longevity: A topcoat can add additional longevity in severely corrosive environments such as marine environments for extended product lifespan and warranty coverage.
- Color: The clear coat can be used to extend the lifespan of vibrant, bright, colorful hues such as bright yellows and reds by providing greater resistance to color fade.
- Graffiti-resistance: Clear coats can also add graffiti resistance when used in certain applications in conjunction with third party products.
It is worth noting that a clear coat can slightly change the visual hue of a color and adds a premium to the product price.
The underside of a metal painted product is usually also painted with a backer. A backer is painted in a neutral color, such as off white, in case it is exposed in applications such as overhang eaves or single-skin agricultural buildings.
This concludes our Understanding of the Constructs of a Metal Finish, the first article in our four-part series on How Architects Can Specify the Right Metal Finish. To learn more about the core constructs of a pre-painted metal finish, see the paint and metal 101 documents at www.steelscape.com/resources/document-library or visit the Architect Center. Look for our next article where we will discuss key color considerations when specifying pre-painted metal.
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