Contending with Corrosion in Metal Exteriors

High-performing, long-lasting, and resilient, PVF film is the technology of choice for corrosive environments
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Sponsored by DuPont™ Tedlar®
By Barbara Horwitz-Bennett
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ARCHITECTURAL FABRIC

Another interesting application of the technology is architectural fabrics for stadiums or as acoustical elements for concert shells. Laminated with PVF film, the fabric has enhanced weather resistance and durability. Applied as a structural fabric used to form tensile surfaces, a fabric membrane is tensioned using cables, wire, steel, or other support.

PVF-coated architectural fabrics are usually thin and lightweight, yet durable. They offer protection from rain, snow, hail, and wind; repel graffiti; and are considered self-cleaning. Of note, PVF film can be laminated with a variety of coated fabrics to form membrane fabric structures at a much lower construction cost than steel.

Architectural fabrics are growing in popularity. They offer design flexibility, functionality, reduced material use, and speed of installation for a wide range of building application. That said, their longevity and sustainability are reliant upon the fabric structure’s ability to withstand the elements and last 20 years outdoors, which is where PVF comes in.

Photo courtesy of DuPont

Two sports domes in the Midwest were constructed for college campuses in 2007. While the dome with PVF film maintained a bright white appearance 15 years later, the non-PVF dome has a discolored, dirty appearance.

In addition to the high level of protection, the PVF film extends the lifespan of architectural fabrics, ensures the fabric meets its performance requirements over its lifetime, protects the fabric against color change over time, and exhibits an extremely low loss of gloss and minimal chalking after 20+ years in the field. And similar to the benefits of metal exteriors with PVF film, it carries protection against harsh chemical cleaning agents, it is easy to clean, and it does not promote the growth of mold or mildew. While architectural fabrics with other protective coatings or finishes do not warranty the appearance of the fabric, PVF film-protected fabrics do have such warranties, ensuring the structure looks new for its lifetime.

Testing done according to ASTM D 1894 standards demonstrates that architectural fabrics with PVF have a lower coefficient of friction than fabrics without the film, ensuring snow-shedding attributes.

Architectural fabrics enable designers to create a wide variety of unique, interesting, and eye-catching roof coverings. They offer the ability to span large areas without columns, support depth and curves, and introduce lighting diffusion in a way that other materials cannot.

Whereas architectural fabrics were limited to white canvas-style appearances in the past, with the application of PVF film lamination, a vast array of colors can be specified, significantly boosting a project’s curb appeal. Glazes and graphics can also be applied, which is particularly desirable for fabric canopies over stadiums where writing or logos require visibility.

Also available as a durable transparent film, the PVF retains its UV protection over time with no loss of color change or adhesion. This is ideal for structural fabrics requiring a high degree of light transmission. When tested for 8,000 hours of UVA-340 exposure with transmittance, the substrate UV protection decreased less than 0.1%. In contrast, competitive PVDF/PMMA bilayer films displayed rapid UV breakthrough with transmittance of greater than 1% in under 3000 hours of UVA-340 exposure. Due to the UV blocking failure, the PVDF/PMMA bilayer films also underwent a severe color change.

When subjected to mechanical property retention testing, the film displays a high retention of mechanical elongation and crack and peel resistance for the transparent top layer.

CASE IN POINT

The aircraft hangar at Logan International Airport was built in 2001 and remains one of the largest frame-supported fabric structures in the world. The PVF top finish can withstand jet-fuel residue and Boston winters, and with its self-cleaning properties, it has needed little maintenance over the years. The approximately 69,000-square-foot fabric-tension structure presents the same appearance as when it was installed.

Another examples is the Beijing Tennis Club. Even though the club constructed three different white air-inflated dome structures with PVF in different years—2006, 2009, and 2014—the three white air-inflated dome structures have maintained identical bright white colors. This is a significant accomplishment in a city known for air pollution, where particulate accumulates on the material over time. In addition to keeping both weather and pollution out, the PVF fabric it also provides enough protection to keep the courts temperature controlled. In comparison, there is a fourth tension architectural fabric structure with a PVDF top finish on the site that discolored and yellowed significantly from its 2003 installation.

Another comparison shows two sports domes in the Midwest, constructed for college campuses in 2007. The dome with PVF film maintains a bright white 15 years later, while the non-PVF dome has a discolored, dirty appearance after the same time period.

For the Saskatchewan Board of Education and Prairie School District’s athletic facility, a multicolor PVF architectural membrane was installed. In addition to providing excellent protection while the interior of the stadium was being built, the nearly 50,000-square-foot insulated structure holds three full-sized basketball courts, an indoor track, a fitness area, multipurpose offices, and concessions, amongst other elements.

An example of a more recent project is in Philadelphia, at Drexel University’s Buckley Field, where the "Buckley Bubble" is protected with a gray PVF film. The large air-inflated structure enables the university to extend its outdoor sports season. Measuring 240 feet by 110 feet with a peak height of 36 feet, the Buckley Bubble is used for softball and baseball, Reserve Officer Training Corps activities, as well as student recreational use. With PVF film protecting the fabric, the bubble is anticipated to appear clean and retain its color for years to come.

PROTECTING INTERIORS

As noted, another popular PVF film application is interiors, particularly higher use environments with greater cleanability and sanitary requirements like healthcare settings.

As a testimony to the long-term protection and durability the technology lends to these applications, Delaware’s Omega Medical Center installed PVF film-protected wall coverings in all high-use areas across the 14,500-square-foot facility over 30 years ago. While the painted sections of the medical occupational health and on-the-job Workers’ Compensation injury center have had to be repainted multiple times over the past three decades, the wallcoverings are as durable, easy to clean, and attractive as they were when the Center first opened back in 1985. While interior design is rarely required to last that long, choosing PVF film enables the designer and building owner to renovate and replace when they want to, not when they have to. This leads to greater design and budgetary freedom, as well as reduced material waste.

More recently, PVF film was selected as a protective material for the renovation of the largest women and children’s medical center in China. Completed this summer, this center in Guangzhou Zeng-cheng was chosen for its durability and cleanability, and applied in three different ways─for interior metal panels, wallcoverings, and wardrobe finishes.

Showcasing the wide range of substrates that the PVF film can be applied to, the material was thermo-formed to the doors of closets, cabinets, and wardrobes in patient rooms, and vacuum sealed to .35-meter-thick PVC, as well as composite wood panels. The film was laminated to a wallcovering patterned with wood, textured grass cloth, and other prints to create a colorful, yet healing atmosphere for this modern medical facility.

CONCLUSION

Rigorous testing and decades of real-world applications have established PVF as a highly robust, protective film well suited for metal exteriors in harsh and corrosive environments. The film is also popular as an architectural fabric, for interiors, and more. Its resistance to cracking, fading, and staining and its high level of color fastness and retention of the surface aesthetic make it ideal for metal siding, roofing, and facades; as a fabric membrane; and for wall coverings and other interior applications.

Compared to other coating technologies, which do not offer nearly the same level of protection on a number of accounts, PVF is ideal for these challenging environments, backed by a long warranty with no geographic limitations. Whether exposed to salt water, pollution, or chemicals, or for settings such as healthcare applications requiring a high level of durability and hygiene, PVF film is the clear choice.

Barbara Horwitz-Bennett is a veteran architectural journalist who has written hundreds of CEUs and articles for various AEC publications. www.bhbennett.com/

 

DuPont™ Tedlar® DuPont Tedlar® PVF films have proven long-lasting protection for interior and exterior architectural applications. Tedlar® superior durability helps safeguard a building from corrosion, pollution or chemical breakdown, and resistance to UV rays. Specify Tedlar® PVF surface protection film to extend the lifetime of metal, architectural fabric, or wall panels for your next project.

 

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Originally published in Architectural Record
Originally published in November 2022


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