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

Learning Objectives:

  1. Identify the unique performance properties of PVF film including durability, longevity, UV protection, formability, adhesion, cleanability, weathering, and chemical and stain resistance.
  2. Discuss key case studies establishing the high-performance qualities of PVF film for metal exteriors.
  3. Establish the life-cycle cost and environmental benefits of PVF film.
  4. Compare PVF’s key performance metrics and tests with coil coating alternatives.
  5. Review other architectural applications that can benefit from PVF film.

Credits:

HSW
1 AIA LU/HSW
ICC
0.1 ICC CEU
IACET
0.1 IACET CEU*
AIBD
1 AIBD P-CE
AANB
This course can be self-reported to the AANB, as per their CE Guidelines
AAPEI
AAPEI 1 Structured Learning Hour
MAA
MAA 1 Structured Learning Hour
NLAA
This course can be self-reported to the NLAA.
NSAA
This course can be self-reported to the NSAA
NWTAA
NWTAA 1 Structured Learning Hour
OAA
OAA 1 Learning Hour
SAA
SAA 1 Hour of Core Learning
 
This course can be self-reported to the AIBC, as per their CE Guidelines.
This course can be self-reported to the AANB, as per their CE Guidelines
Approved for structured learning
Approved for Core Learning
This course can be self-reported to the NLAA
Course may qualify for Learning Hours with NWTAA
Course eligible for OAA Learning Hours
This course is approved as a core course
This course can be self-reported for Learning Units to the Architectural Institute of British Columbia
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Causing the country more than a trillion dollars in damages each year, corrosion is a major issue to contend with. Occurring as a natural process, oxides develop over time, weakening materials and making them vulnerable to a variety of performance and protection issues.

Photo courtesy of CMP (Construction Metal Products) and Metal Alliance LLC

A new 6,700-square-foot metal roof, protected by highly durable PVF film, was installed at the Sea Crest Condos in Hilton Head, S.C., replacing the previous PVDF-coated roof which had become corroded over time due to the high salt spray environment of its coastal setting.

Metal exteriors are particularly vulnerable, especially in corrosive environments such as areas of exposure to salt spray (coastal regions) or certain chemicals and off-gassing (manufacturing facilities, chemical plants), where this type of deterioration can occur ten times faster than in average environmental conditions.

Defined as a chemical or electrochemical reaction between a material and its environment, corrosion causes deterioration of building materials and its properties over time.

As the protective layer, typically a paint or coating, begins to exhibit cracks and peeling, the exterior is left exposed to reduced mechanical strength, structural damage, and potentially reduced seismic performance. If the structure is compromised, the resulting required repair work can be substantial, causing a significant financial expense to building owners, not to mention the environmental considerations of rebuilding and repair.

Fortunately, corrosion is preventable, as Joseph Crissinger, CSI, CCS, CCCA, ASQ, a Spartanburg, S.C., construction specifications, materials, and building systems consultant, explains, “Isolating the metal or substrate from unacceptable conditions will usually prevent corrosion. That is where the proper protective (corrosion-resistant) coating comes in.”

THE RIGHT COATING FOR CORROSIVE ENVIRONMENTS

While a number of exterior coating products offer a certain level of protection from these challenging environments, few are truly capable of shielding exteriors in these harsh settings. So, while some of the different paints and coatings may be sufficient under ordinary environments, when it comes to highly corrosive and coastal settings, a more robust solution is needed.

Polyvinyl fluoride (PVF) is a highly durable fluoropolymer used in films and coatings that provides an exceptionally long-lasting finish to a wide variety of surfaces exposed to harsh environments. Not only do these protective films and coatings meet specifications for AAMA 2605, but the real proof of the pudding lies in the fact that this technology has been successfully protecting surfaces around the world for the past 60-plus years.

PVF polymer has been used in coatings that protect brake tubes and fuel lines in automotive applications due to its flexibility and resistance to rock spray and salt corrosion. PVF also has a long history of being made as a film, which has been specified into aircraft interiors since its invention due to its cleanability, durability, and excellent fire and smoke ratings.

Used for interior sidewall decorative panels, window shades, lavatories, bulkhead partitions, and more, the film offers a high level of interior design flexibility. PVF can be embossed and printed, supporting many texture designs, and can be tailored to various gloss levels, thicknesses, and finishes.

Photo courtesy of DuPont and Metal Alliance LLC

Demonstrating the durability of PVF film, the top part of this plant 's metal roof has remained pristine after more than eight years, whereas a two-year-old alternative coating shows considerable corrosion.

PVF film also has long-term track record protecting buildings. In fact, the film has demonstrated an unusually high level of long-term performance and durability in various highly corrosive environments.

Take the Okinawa power plant in Japan, for example. Situated less than 1,500 feet from the coastline in a high salt spray environment, and exposed to power plant smoke since 1986, the exteriors essentially look the same as they did upon installation 27 years ago. The PVF film-laminated walls and roof still deliver the same level of corrosion and protection. The plant has experienced practically no color fade as well, and has not required replacement of any panels.

The specification of such a long-term solution offers clear sustainability benefits. The extraction and manufacturing of steel or other metals occurs once and lasts for decades. The life-cycle embodied carbon, in turn, is significantly lessened, as the lifespan of each panel is increased, necessitating less material replacement over a building's lifetime.

Testing and other long-term case studies have also demonstrated an extremely high level of resistance to harsh weather, UV light, chemicals and pollution. PVF film is highly resistant to stains, and is easy to clean and disinfect. As a dirt-shedding material, it retains a new, fresh appearance and doesn't require freshwater rinses in warrantied exterior applications. Due to its hardiness and cleanability, PVF film is also a great solution for wallcoverings in high-traffic, sterile environments like hospitals and healthcare facilities, as well as restaurants, hotels, and airplanes.

Photo courtesy of DuPont

DPVF film offers a wide range of colors, matching popular coil coating colors, and transparent UV-resistant film.

METAL EXTERIORS

PVF film has distinguished itself as a superior solution for metal facades and roofs, particularly in harsh coastal environments with prolonged exposure to saltwater.

The polymer is highly inert, which makes it resistant to a wide variety of corrosive and chemical agents. It absorbs very little visible or UV light and is therefore highly resistant to photolytic degradation. Strong, flexible, and fatigue-resistant, the polymer is made without plasticizers and therefore does not promote growth of mold and mildew.

The material meets ASTM testing and performance standards including UV resistance, moisture absorption, strength, flexibility, clean ability, weathering, chemical and stain resistance. In addition, the film meets stringent smoke and fire codes.

Whereas paint requires a more involved application process, with a primer, topcoat, and often a third clear coat for extra protection, PVF film is applied via a single layer lamination process. The film, with adhesive, is laid down onto the metal coil and baked through an oven, setting the adhesive. The film is then part of the metal system, just as a coating would be, requiring no solvent drying time, or additional passes.

Since metal is particularly vulnerable to corrosion, building owners in coastal settings really have to consider the best level of protection for the roof and cladding. While some coil coatings can offer good protection, they are unable to meet the performance level of PVF film. Ultimately, corrosion will start to eat away at the integrity and appearance of the metal exteriors. The panels will need to be repainted, or more likely, replaced entirely. Not only will owners incur this expense, but the use of resources is an environmental strain. In addition, albeit temporary, the restoration process may disrupt the building’s regular operations and ability to run its business.

When PVF film is the protective layer of choice, the building is then set up for long-term protection, backed by up to 50-year warranties, with no coastal restrictions. In harsh operating environments such as steel mills or chemical plants, replacement of interior panels is expected and budgeted for every two years, sometimes less. Using PVF film, these interior panels can last upwards of eight years without damage, significantly reducing the time and cost of frequent replacements, as well as reduced waste over the buildings lifetime.

The composition of the PVF also lends a high level of flexibility and formability for enhanced adherence to the substrate. Cracking and corroding often happens on the bent part of formed panels. PVF is inherently extremely flexible, bending to 0T without any issue. This flexibility means the film does not crack or weaken when formed, so protection remains uniform across all bent edges and panel shapes.

Highly flexible, PVF film is available in a wide range of colors matched to popular coil coating colors, as well as transparent UV-resistant film. Ranging from cool colors like spruce green and sky blue; to neutral hues such as shell white, charcoal gray, dark bronze, and matte black; to warm colors like concord cream and sandstone, PVF film combines long-term durability with high quality aesthetics.

Leveraging its excellent color uniformity and fade resistance, PVF film-coated surfaces maintain their original appearance for decades.

 

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Originally published in Architectural Record
Originally published in November 2022

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