This course is part of the Metal Architecture Academy

Durable, versatile, and long-lasting, Metal Composite Material (MCM) is an increasingly popular design option for cladding walls in a range of building types.

With a high recycled content, the panels are easy to fabricate in a wide array of shapes and textures and are easy to install. The affordable material is lightweight, thereby minimizing structural loads on the subframe and subframe material costs. MCM is specified with a flame-retardant core to meet mandated NFPA 285 testing requirements.

While the material’s performance benefits are well established, MCM’s reputation as a bold, exciting, and creative material that architects can craft into colorful, shaped, perforated, and textured designs has been steadily gaining traction.

To help unlock all this creative potential, there are many standard finishes suitable for MCM; solids, micas, metallics, prismatics, shimmer effects, wood, stone, and more. MCM sheets are always factory-finished, ensuring a high level of consistency and quality. Custom color paints are available, as are specialty finishes like faux wood grain, faux stone, terracotta, color shifting, and textured finishes.

“Finish type is particularly important in specifying MCM panels,” confirms Kevin Le, design professional, Laurence Group, St. Louis. The composition of all the exterior materials ultimately becomes the impression that represents the owner/company/entity to the general public. Contemporary versus traditional, lightness versus heftiness, slick versus organic…finishes have the power to transform these powerful ideas into real life tangible icons that exist within the community.”

To deliver high-quality, color-consistent designs by selecting the right finish for a project, an understanding of the technology and standards regulating these projects can help designers bring their MCM facades to life.

Photo courtesy of Sobotec

The bright white finish on MCM panels on this grand addition to the Las Vegas Convention Center stays shiny and bright, even in the extreme desert sun.

THE PAINT SYSTEM

Breaking things down, paint systems for MCM are comprised of three main components: the pigment, solvent, and binder. The pigment is made of tiny, solid particles which determine the color based upon the levels of transmitted and reflected light. The solvent is the carrier where the pigment and other substances are suspended giving the paint its desired viscosity. And the binder is the resin that holds everything together. The formulation also includes additives to enhance the paint’s properties and/or improve the manufacturing and application process. The complex interactions between these components determine the paint’s properties including color brightness, level of opaqueness, coverage, permeability, and abrasion resistance. Pigments can be inorganic or organic, which determines the finish composition, characteristics, and appearance.

Inorganic pigments are manufactured from mineral compounds, mainly complex metal oxides. They are opaque and lend a high level of color stability, heat, and chemical resistance. These pigments produce more neutral colors and earth tones such as beige, brown, and tan. While the color range is more limited, the inorganic pigments have the advantage of stability and don’t bleed. They are also compatible with almost all polymers.

Organic pigments are carbon based, often made from petroleum compounds. They are transparent and can produce bold, vivid colors. However, they allow UV rays and oxygen to penetrate and have a lower resistance to fade, and heat. Organic pigments may also have a lower gloss retention.

For the best of both worlds, pigment formulations often include a blend of both inorganic and organic pigments. The pigment blend also determines wavelength-selective absorption, special effects, and the benefits of cool pigment technology, if desired. Some special effects include pearlescent, color-shifting, and high-sparkle pigments using materials like tiny flakes of aluminum or mica.

By employing cool pigments in a coating, a wall experiences lower levels of solar heat gain. The wall stays cooler, thereby impacting interior temperatures and reducing air conditioning loads. Cool pigmentation offers designers a broad range of colors, including darker hues, and helps mitigate the heat island effect of heat buildup in urban areas. The solar reflectance index (SRI) is the value which determines how cool the finish is. Combining the amount of heat-inducing radiation that is reflected off the surface with emissivity, which is the level of heat that the surface can dissipate, a value of 0 to 100 is determined.

Photo courtesy of Robert Stefanowicz Photography/3A Composites USA

The high-gloss red finish on the MCM panels used on the Great Northern Way Pavilion in Vancouver, B.C., dazzles visitors with its brilliance.

FINISH SYSTEM TYPES

To provide the high levels of performance associated with MCMs, these coatings are typically comprised of high performing resin chemistries. The most common resins for these applications are polyvinylidene fluoride (PVDF), super-durable (SD) polyester and fluoroethylene vinyl ether (FEVE). These coatings fall under two categories: thermoset, which includes polyester, FEVE, and thermoplastic like PVDF. The former contains clear resin bases, which support a wide range of colors and glosses. Once thermosets are cured, they present a very even, stable appearance even when exposed to heat or pressure. Thermoplastics are typically 70 percent PVDF resin-based and provide superior UV resistance to all the other paint systems. The color ranges to more earth tones and offers typical gloss ranges of 25 to 35.

PVDF coatings have been around for over 50 years and offer high performance. PVDFs are highly resistant to UV radiation, corrosion, and chemical attack, and provide a finish warranty of up to 30 years. PVDF comes in a wide range of colors and finishes, including metallic and pearlescent finishes, and provides a high level of color and gloss retention. “We most often specify PVDF coating for our projects due to its long-term record for reliable durability,” relates Drake. FEVE coatings offer a high level of color and gloss retention. As a thermoset finish, the formulation works well in high gloss applications. FEVE is also resistant to chemicals, corrosive atmospheres, and UV rays, making it very weatherable.

As high-performance finishes, PVDF, and particularly FEVE, do come with a price tag, but their long-term durability and quality often make the investment worthwhile. Both MCM coatings are commonly found in various applications including restaurants, banks, car dealerships, schools, and corporate office buildings.

“We’ve specifically targeted FEVE coating when we are looking for a similar level of high performance that also achieves an unmatched gloss for the finished installation,” relates Drake.

Another area where the two coatings differ is how long they’ve been around. While PVDF coatings have been available for over 50 years, FEVE is a newer product. FEVE and PVDF also offer a longer projected lifespan and comparable warranties.

The third option, SD polyesters offer good impact, scratch, and abrasion resistance, present a smooth finish, and are more affordable. However, they don’t do as well in the weather resistance category. Typical SD Polyesters in all color families meet AAMA 2604. In certain color families, SD Polyester will approach or meet AAMA 2605 requirements.

To help select the right finish for a project, Lee Rubenstein, AIA, LEED AO, a principal with Washington, D.C.-based R2L: Architects explains that at baseline, the finish must be durable and stable, and it must meet industry warranty standards. “Beyond that, we want to understand how the panels will look under a range of conditions—direct sunlight, in shadow, at night, wet, dusty, up close or from afar,” she says. “This helps to understand whether the finished work can meet the design intent.”

For JRA Architects, the firm’s large institutional client base makes long-term performance a priority on many of their projects. Consequently, the architects are taking a hard look at weather and fade resistance when specifying MCM coatings. In addition, Drake points out that many MCM panel applications are near grade, further emphasizing the importance of durable finishes.

Another consideration is selecting a two-coat vs. a three-coat finish. Typically, a two-coat system consists of a primer and topcoat and a three-coat system adds another clear coat over the top color coat. While the two-coat application can be produced through one pass in a commercial coil coating line, the third coat usually requires a second pass. Most MCM manufacturers provide stock selections of two-coat and three-coat finishes as an industry standard. Custom colors are available in two and three coat finishes and typically subject to longer lead times and additional costs based on color volumes. Consequently, specifiers should consider the additional cost and lead time for custom colors orders.

In terms of color quality, in most cases, a two-coat system is sufficient. That said, there are cases where the extra coat is recommended to upgrade the color retention and chalk resistance of a solid or metalescent base color. For example, this could be the case for saturated colors such as red, orange, purple or metallic colors like bright silver to protect the aluminum flake from losing its brightness. Also, some special effect coatings might need an effect coating on top of the primer and base color coat. Another reason architects might choose a three-coat system is to have the benefit of a broader palate of finishes, including micas and metallic. It’s important to note that despite the added layer and cost, three-coat systems don’t offer a longer warranty.

Photo courtesy of 3A Composites USA

With a two-coat PDVF bright white finish, this Norwegian Cruise Lines Terminal in Miami is as striking as the ships that dock near it.

Photo courtesy of MG McGrath

PDVF goes to college. MCM panels finished with charcoal fluoropolymer finish gives this campus building a sophisticated look at Carleton College in Northfield, Minnesota.