Polyvinylidene Fluoride Coating Failures
Karim Allana, RRC, RWC, PE
Allana Buick & Bers, Inc. | Palo Alto, CA

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Karim Allana, RRC, RWC, PE
Allana Buick & Bers, Inc. | Palo Alto, CA
Karim Allana, RRC, RWC, PE, is the CEO and founding principal of Allana Buick
& Bers Inc., an architectural-engineering firm specializing in the building enclosure and
sustainable construction. Allana has been in the architectural-engineering and construction
fields for more than 35 years and acted as a consultant and expert witness in over 450
construction-defect projects. He earned a bachelor of science in civil engineering from
Santa Clara University and is a licensed professional engineer in California, Washington,
Oregon, Nevada, North Carolina, and Hawaii. He is also a Registered Roof Consultant
and Registered Waterproofing Consultant through IIBEC.
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ABSTRACT
SPEAKER
Polyvinylidene fluoride (PVDF) coatings have been a reliable part of construction since the s, but over the
past 15 years, we have witnessed an increasing number of premature PVDF coating failures. This paper will review
changes the industry made that led to these failures and how to avoid them through proper specification and testing.
This paper will demonstrate that the failures can be attributed to changes in the industry's use of chromium phosphate
pretreatment wash'the tried and true method. The American Architectural Manufacturers Association's specification
AAMA initially included chromium phosphate wash as a mandatory requirement. However, because
there are concerns about the environmental impact of chromium, manufacturers' use of the wash became voluntary
in . Alternative washes such as phosphoric acid are being used instead of chromium phosphate, leading to poor
adhesion and a lack of corrosion protection.
This paper will also review the steps and costs involved in repair and recoating procedures, and how to modify
technical specifications and implement testing to mitigate premature failure.
Polyvinylidene fluoride (PVDF) coatings
come in a variety of colors and finish options,
have high chemical and ultraviolet resistance
and excellent resistance to everyday wear and
tear, and can even self-extinguish during a
fire.They can also be cohesive with virtually
any architectural style. PVDF coatings can be
specified as a two-coat or three-coat system,
ranging in thickness from 30 microns to 40
microns. The corrosion inhibiter primer is
generally 5 microns. For better scratch resistance
for roof panel application, specify a
three-coat process.
However, over the past 15 years we have
witnessed an increasing number of premature
PVDF coating failures. All major manufacturers/
fabricators are aware of this issue but are keeping
it quiet until they can address it satisfactorily.
While coating failures may sound relatively
benign compared with other building issues,
the cost of repair can be very significant. Issues
range from coating delamination to high levels
of aluminum corrosion, especially in coastal
areas, where it can cost tens of millions of dollars
per building to repair.
This study will go into the fundamental
changes the industry made that led to these
failures and how to avoid them through proper
specification and testing. We will also cover
the predecessor and predominant alternative
to PVDF coatings'anodized aluminum'and
why PVDF coatings can still be the better
option despite the increased failure rates.
Finally, this study will review coating
repair/recoating procedures, the steps and
costs involved, how to modify technical specifications
for new construction, and how to
implement postapplication testing to mitigate
premature failure.
THE RISE OF ARCHITECTURAL
ALUMINUM AND METAL FINISHES
When architectural aluminum arrived on
the scene in s, it was hailed as a modern
marvel and a sign of a major advancement
in construction. However, pure aluminum is
not strong enough for architectural use, but
aluminum alloys (typically aluminum mixed
with silicon or copper) are ideal.1 Due to its
light weight, light color, structural integrity,
and durability, architectural aluminum is commonly
used for exterior building elements such
as curtain wall extrusions, window frames,
spandrel panels, decorative façade features,
and metal roof panels.
Most aluminum extrusion manufacturers
provide PVDF coatings for their extrusions.
Naturally occurring oxides on uncoated
aluminum surfaces are susceptible to various
forms of corrosion that can compromise the
aluminum. In most cases, a protective coating
or metal finish is added to prevent corrosion
and increase the lifespan of the metal.
There are two primary types of architectural
metal finishes in use today that this
paper will focus on: anodizing and PVDF
coatings. While there are pros and cons to each
finish type, they both result in more durable,
corrosion-resistant metal and provide color
and finishing options. Choosing the right
architectural finish for a project can affect warranty
duration, durability, and overall system
longevity.
ANODIZING 101
Before the inception of PVDF coatings,
anodizing was the preferred choice for an
attractive and durable architectural finish.
Color availability with anodized finishes is
generally limited to bronze, clear, black, and
champagne.
Anodization is an electrochemical process
that increases the thickness of that oxide layer
that protects the base metal. Anodization creates
a 'conversion coating.' It literally converts,
or alters, the aluminum surface (as compared
with a topical application, such as
paint). This makes the aluminum
more durable, corrosion resistant,
scratch resistant, visually attractive,
and flexible during fabrication.
Anodized aluminum first appeared in
industrial applications in the s,
but it was not until the s that it
became hugely popular for architectural
use.2
To oversimplify a complex electrochemical
process, anodizing involves
submerging an anode and a cathode
in an acid electrolyte (chemical
solution), then passing an electrical
current between them. The current
releases hydrogen at the cathode causing
reduction and releases oxygen at the surface of
the anode, creating oxide buildup or oxidation.
When anodizing aluminum, the aluminum
acts as the anode'hence the term anodizing.
The oxide buildup acts as a protective layer.
There are different primary types of anodizing:
Type I, Type II, and Type III. Each type
utilizes a different acid electrolyte for different
physical and chemical traits.
' Type I or chromic acid anodizing
(CAA) was initially known as the
Bengough-Stuart process. It was first
used industrially in to protect
Duralumin seaplane parts from corrosion.
Today, it is most often used
in aerospace and military defense
applications. Unfortunately, CAA has
limited utility for decorative or exterior
building applications due to its naturally
dark color.
' Type II or sulfuric acid anodizing
(SAA) is the most common method.
Only 33% of the coating sits above the
substrate; the other 67% directly penetrates
and integrates with the aluminum
substrate. This makes it extremely
hard and durable. Additionally, the
porous nature of the aluminum oxide
readily accepts paints and lacquers,
making it ideal for decorative and exterior
building applications.
' Type III or hard/hardcoat anodization
also uses sulfuric acid as the electrolyte,
but it produces a much thicker
II BEC International Convention & Trade Show | September 15-20, A l lana | 163
Polyvinylidene Fluoride Coating Failures
Choosing the right
architectural finish for
a project can affect
warranty duration,
durability, and overall
system longevity.
coating than Type I or II anodization. Type III coatings have excellent corrosion resistance, but mediocre chemical resistance. Therefore, it is not commonly used for architectural finish applications. Type III is typically specified for applications with extreme potential for wear and tear, such as mechanical valves and pistons.
Architectural aluminum extrusions are typically Type II anodized and are commercially available in either Class I or Class II. Class I has a minimum finish thickness of 0.07 mil (0. microns), while Class II has a finish thickness of 0.04 mil (0.001 microns).3 Thicker coatings spend more time in the processing tanks to give them that heavier coating.
MANUFACTURING OF ANODIZED ALUMINUM EXTRUSIONS
The commercial manufacturing process for anodized aluminum has several steps. Once several racks' worth of extrusions are ready to be anodized, they first need to be cleaned with an alkaline solution to remove debris, oils, or other contaminants from the aluminum surface. The next steps are the alkaline etching and desmutting processes. Etching involves dipping the racks into an acidic solution to reduce the appearance of minor surface defects. Desmutting is the process of removing excess metal from the aluminum surface after etching.
Finally, the extrusions are ready to be anodized. Typically, this involves the extrusions being immersed in 15% sulfuric acid solutions and charged with an electrical current to form the aluminum oxide layer. The longer an extrusion is immersed in the anodization tank, the thicker the oxide coating.
Once the aluminum oxide layer is formed to the desired thickness, color is added by electrodepositing various amounts of tin for various colors. As mentioned previously, anodized aluminum extrusions are typically available in clear, black, champagne, and various bronzes. The last step is the sealing process, which closes the aluminum oxide pores. This coat helps protect the oxide layer and color layer from the elements. There are multiple sealing options. The most common processes use deionized water, potassium dichromate, and nickel acetate.
SPECIFYING ANODIZED ALUMINUM AND
WARRANTY CONSIDERATIONS
ASTM B580-79(), Standard Specification for Anodic Oxide Coatings on Aluminum,4 is used to specifiy anodized oxide coatings for aluminum. There are several considerations when specifying anodized aluminum for architectural use: aluminum dimensions, corrosion resistance, air pollution/salt levels, up-front costs versus eventual repair costs, aesthetics, and more.
Due to shorter warranties, inability to perform field repairs, lack of color availability, lack of color uniformity between batches, and inferior performance, anodized aluminum is not as commonly specified for architectural purposes. Additionally, anodized aluminum does not have a high chemical resistance. It can be affected by acidic air pollutants, especially in coastal areas. Generally, in coastal areas, it is best to specify anodization that is thicker than Class I, up to 10 mil.
Since the s or s, most projects have chosen PVDF coatings over anodized window and curtain wall extrusions. However, anodized extrusions are still specified for midrange storefronts or lower-cost building exteriors, such as for schools or local municipal buildings. Anodized aluminum is also commonly used for large custom shapes, such as screens, handrails, and artwork, that can be dipped in tanks similar to hot-dipped galvanizing.
Most manufacturers offer a standard one-year warranty on anodized aluminum extrusions, with some five-year or 10-year warranties available from select manufacturers (Table 1).5'7
ANODIZED ALUMINUM FAILURES
There are at least 14 types of aluminum corrosion methods. The predominant form of aluminum corrosion is atmospheric corrosion. This is loss of material due to wind-driven abrasives. The relative softness of the aluminum makes it particularly susceptible to this form of corrosion. Anodization is one method of protecting the aluminum. As mentioned above, it chemically alters the surface of the aluminum to a hard oxide, which can withstand the effects of atmospheric corrosion.
Many of the other forms of aluminum corrosion involve water and the difference in electrical potentials, which are set up in the form of dissimilar metals, salts, or microscopic grain boundaries. Exposure to harsh environments (such as alkaline atmospheres or salty ocean spray) can leave anodized aluminum susceptible to corrosion if water is present. The conditions erode the protective oxide layer, leaving the aluminum vulnerable.
Figures 1 and 2 show a lanai railing replacement project for an 11-building, 364-unit residential development in Ka'anapali, Maui, Hawaii. Figure 1 shows significant corrosion on the anodized aluminum guardrail. The extent of the corrosion differed from unit to unit. A possible reason for this could be that certain railings were cleaned more than others, which unevenly removed salt deposits (chlorides).
Additionally, we observed that galvanic corrosion was taking place on the railings due to the materials used, even though it is not easily visible. Not visible in Fig. 2 is the galvanized steel fastener securing the base of the aluminum railing picket to the aluminum rail. Salt-laden rainwater trapped at the base of the picket likely set up the galvanic reaction with the steel fastener (Fig. 3).
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Table 1. Anodized architectural aluminum statistics and specifications
Coating/oxide thickness (ASTM B244/B487)
'
' Class I
0.07 mil / 0. microns
' Class II
0.04 mil / 0.001 microns
Coating/oxide weight (ASTM B137)
'
' Class I
4.18 mg/cm2
(27.0 mg/in.2)
' Class II
2.40 mg/cm2
(15.5 mg/in.2)
Corrosion resistance (ASTM B117)
'
' Type II (Class I)
Excellent
( hr of exposure)
' Type II (Class II)
Intermediate
( hr of exposure)
Common warranty duration
One year standard
The consultant, Allana Buick & Bers, was retained for a railing replacement project at a nine-story, 463-unit residential building in Lahaina, Maui. Several anodized aluminum railings showed typical signs of corrosion and some pinholing. In addition, we also observed white rust and hazing along the bottom rail. This is a common indicator of corrosion of the fasteners and a dissimilar metal reaction.
Unlike PVDF coatings, anodized aluminum cannot be repaired in the field. Each piece must be replaced. While this is not cost prohibitive for individual balconies or lanai, it is not a practical option for most building exteriors.
PVDF COATINGS 101
PVDF is a nonreactive thermoplastic fluoropolymer (plastic) used in high-performance architectural coatings. PVDF's coating properties, such as high chemical resistance, ultraviolet resistance, mechanical strength, color/gloss retention, and ease of processability, make it a superior alternative to regular paint for coating metal. Unlike anodized aluminum, color options are virtually limitless. Additionally, PVDF coatings are uniform in appearance, unlike anodized finishes.
PVDF coatings came into use in the s for use in coating mechanical parts. It was not until the s and s that they came into use for architectural purposes. They reached peak popularity in the s and s and have now become ubiquitous for both commercial and residential applications.
Architectural PVDF coatings are resin based and come in a variety of proprietary and nonproprietary formulas. Different PVDF-to-resin ratios and additives produce different architectural properties.
Seventy percent PVDF coatings (that is, a makeup of 70% PVDF and 30% resin) are the most weather resistant, chemical resistant, and fade/chalking resistant. These are most often used for high-performance building exteriors. They are not recommended for roof panel applications, where additional longevity and scratch resistance are desirable. While not as durable as 70% PVDF coatings, 50% PVDF coatings are still a viable (and less expensive) alternative for certain less-demanding architectural applications, but typically not for high-performance building exteriors. Seventy percent PVDF coatings meet AAMA standards.8 Fifty percent PVDF coatings do not. They meet the less-stringent AAMA requirements.9
MANUFACTURING AND APPLICATION OF PVDF COATINGS
PVDF is typically synthesized by the polymerization of monomers of vinylidene difluoride. This process was originally developed in the s. The reaction takes place in a temperature-controlled, pressurized emulsion. The resulting material is processed for various applications. Pure PVDF, in its powder form, is the key ingredient in PVDF architectural resin coatings.
PVDF coatings are available in liquid (wet) coatings and powder (dry) formulations. While powder coatings are generally cheaper, wet coatings are typically preferred for exterior architectural use because powder coatings are not ultraviolet resistant. Additionally, mica and other metallic-based colors are not available in dry/powder PVDF coatings.
The wet PVDF coating application requires a precise, multistep process. After an initial hot alkaline cleansing wash, PVDF coatings require a chemical conversion coat for the aluminum surface area prior to application. The conversion coat protects the metal from
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Figure 1. Corrosion (white oxide layer) on anodized aluminum guardrail.
Figure 2. Galvanic corrosion on anodized aluminum guardrail.
Figure 3. Steel angles used to repair aluminum pickets.
corrosion. Additionally, it operates as a binder between the aluminum substrate and the color top coat by adding significant surface area between the two coats.
Historically, the process relied on a chromium phosphate (CP) or chromium chromate (CC) conversion coat, but AAMA revised the standard in to allow non-chrome alternatives. These are discussed in detail later in this paper.
After a surface has been pretreated, there are three types of multilayer spray coating systems: two-coat, three-coat, and four-coat. Two-coat and three-coat are the most common systems for exterior architectural applications. Each layer requires 10- to 15-minute curing intervals between each coating layer at between 230˚C and 250˚C.10
' One-coat (primer): The conversion coat is typically 5'10 microns thick. It adds increased durability and protection for the aluminum substrate and increases adhesion between the primer and additional coats.
' Two-coat (color top coating): The color top coating is typically the thickest layer and is generally 25'30 microns thick. This layer adds enhanced durability in addition to decorative color.
' Three-coat (clear top coating): A clear top coating is generally 10'15 microns thick. This layer adds even more protection and increases color retention and luster.
FORENSIC ANALYSIS
OF INCREASED PVDF
COATING FAILURES
Until recently, there appeared to be few downsides to specifying PVDF coatings. In our capacity as a forensic expert for construction defect litigation specializing in the building enclosure, Allana Buick & Bers has personally observed the increase in PVDF coating failures. We have been investigating failed building exteriors for more than 30 years. The rate of PVDF coating failures has significantly increased in the past 8'10 years alone. Because these systems are expected to last 40 to 50 years before recoating, failures within 10 years of application represent a significant loss of product life expectancy.
Common modes of failure include filiform, discoloration, bubbling, cracking, and delamination from the aluminum surfaces. Filiform corrosion is when the aluminum starts to corrode at the edges and the moisture and corrosion spread under the coating in a tiny wormhole. Filiform corrosion is not easily detectable and can pop up 12 to 24 in. away from the aluminum edge.
Failure of protective coating allows for premature degradation of the aluminum extrusions and reduction of useful life. To make matters worse, many coating issues initially go undetected. To spot them on mid- and high-rise buildings, there typically needs to be an intentional survey with exterior building swing stage drops.
As we investigated more and more instances of PVDF coating failure, we began to suspect that there was a more systemic issue rather than simply a rash of manufacturing defects and improper applications.
One of the more prevalent instances of PVDF coating failure we observed was at a 419-unit, 58-story residential high-rise in San Francisco, California. The building consists largely of an aluminum-framed curtain wall system and aluminum panels and was completed in . Allana Buick & Bers was retained to investigate exterior building defects and from a swing stage, we were able to document widespread coating failure. We observed PVDF coating failures at both horizontal and vertical framing members.
Figure 4 shows the individual instances of coating failure ranging from the top to bottom of the east and west building elevations. The red boxes indicate sample drop zones for our inspection. The black dots indicate observed areas of coating failure. We also performed drops on the north and south elevations and observed a similar rate of failure. Due to the sample size of our visual observations and high rate of failures, we determined that the coating failure issue was widespread.
Figures 5 and 6 show some typical examples of severe corrosion and bubbling at the aluminum curtain wall frames. Forensic testing found chromium present on some samples but not others. This led us to determine that while a chrome-based primer was applied, it was either not applied uniformly or not applied in the specified amount.
To remediate the coating failure (and other
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Figure 4. Prominent coating failure at east/west building elevation drops.
Figure 5. Polyvinylidene fluoride coating failure: Corrosion at aluminum curtain wall frame.
Figure 6. Polyvinylidene fluoride coating failure: Corrosion at aluminum curtain wall frame.
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façade defects), we recommended installing an overcladding over 100% of the existing curtain wall. The overcladding consisted of manufacturing new aluminum break metal to completely envelope the existing extrusions. The cost to rectify these coating failures for the entire curtain wall façade was estimated at $45,476,874.
Another recent instance of widespread PVDF coating failure was at a 108-unit, 21-story, podium-style mixed-use residential building, also in San Francisco. Generally, the building consists of precast concrete panels, stucco walls above the roof, and aluminum-framed window wall assemblies.
During a visual investigation of the window wall assembly, we documented various PVDF coating failures at the aluminum framing and at tie-back anchor ports. Figures 7 through 9 show some typical examples of severe corrosion and pitting observed at the aluminum window wall frames and tie-back anchor ports during swing stage drops. We ultimately concluded that the conversion coating used did not include CP or CC.
To remediate the coating failure, we recommended removing 100% of the exterior coating, then recoating the entire window wall system. The cost of recoating all the aluminum framing was estimated at $1,838,720 (not including other building repairs).
While the previous instances were wet PVDF coating failures, we have also witnessed PVDF powder coating failures. Figures 10 and 11 show some typical examples of dry PVDF coating failure at a 99-unit, nine-story residential building in San Francisco. We observed severe discoloration of the PVDF coating at
Figure 7. Polyvinylidene fluoride coating failure: Corrosion at aluminum window wall frame.
Figure 9. Polyvinylidene fluoride coating failure: Corrosion at window wall tie-back ports.
Figure 8. Polyvinylidene fluoride coating failure: Corrosion at aluminum window wall frame.
Figure 11. Polyvinylidene fluoride coating failure: Significant corrosion at window flashings.
Figure 10. Polyvinylidene fluoride coating failure: Significant corrosion at window flashings.
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the window ledge flashings, and similar exterior door frames. In Fig.. 10 and 11, significant corrosion at the window flashings is visible. We ultimately concluded that several factors were responsible for the premature failure. Just like with the liquid PVDF coating failures, we suspected the cause of failure was the pretreatment wash. In this case, we found that the prewash was not CP, primer was not applied properly, the coating was of improper thickness, and a lack of proper surface preparation led to trapped contaminants.
The cost to recoat exterior aluminum at the window frames, fixed windows, window system mullions, and door sash/frames was estimated at $2,924,123.
' Primer/conversion coat application: $433,428
' High-performance top coat finish/PVDF coating applications: $1,787,815
' Sealant removal and replacement: $702,880
' Total coating repairs: $2,924,123
WHY PVDF COATINGS ARE
FAILING . . . AND HOW TO
DO TO PREVENT IT
As mentioned above, PVDF coatings historically relied on a CP or CC conversion coating. From (AAMA 605.2)11 to (AAMA -2), the CP/CC conversion coat was a mandatory requirement for PVDF applications. The standard mandated 40 mg per square foot of CP or CC for the aluminum surface area. In , AAMA revised the standard to allow non-chrome conversion coating alternatives (AAMA -05). These changes were made due to safety, environmental, and cost concerns.
The Occupational Safety and Health Administration (OSHA) also issued new standards in that significantly lowered allowable limits for human exposure during the manufacturing process (. ' Chromium [VI]). The permissible exposure limit was reduced from 52 micrograms to 2.5 micrograms per cubic meter of air over an eight-hour period.
Due to the combination of safety/environmental concerns and increased costs of OSHA compliance, insurance costs for manufacturers went up considerably. This resulted in most PVDF coating manufacturers choosing nonchrome alternatives. Unfortunately, we are learning that chrome-base pretreatment was the key to PVDF coatings' longevity, durability, and color retention. The other phosphate alternatives really did not work. Manufacturers are now experimenting with nickel and other types of prewash systems that are not yet commercially available. The key to preventing premature PVDF coating failures is to ensure a CP/CC conversion coat is used and that specific quality assurance/quality control (QA/QC) materials testing is performed to verify CP/CC content and coating thickness.
Specifying PVDF Coatings to Prevent Premature Failure
ASTM D, Standard Specification for Unmodified Poly(Vinylidene Fluoride) (PVDF) Molding Extrusion and Coating Materials,12 governs PVDF coatings. Since the s or s, most anodized architectural finishes have been replaced with PVDF coatings, particularly in mid- and high-rise buildings.
There is currently an ASTM committee reviewing these standards in light of the increased failures. While the committee deliberates, several steps can be taken to proactively mitigate premature PVDF coating failure.
Based on our field observations and forensic analysis, we recommend modifying the technical specifications for all aluminum extrusions to mandate the use of a chrome-based conversion coating, including when used for metal panels and roofing. To ensure proper application, QA/QC testing should be mandated at the coating application plant and on-site.
We recommend specifying ASTM D testing. ASTM D is the test method to determine how much chromium is deposited through the conversion coating using X-ray fluorescence spectroscopy. We also recommend using a spectrophotometer to confirm color and gloss uniformity (Table 2).
THE COATING REPAIR PROCESS
There is a reason preventing premature coating failure is so critical: it can be extremely costly to repair and can be detrimental to a building's integrity if ignored. Luckily, PVDF coatings can be repaired in the field. While the process itself is not complicated, the coating repair process can be time consuming and very expensive.
Figure 12. The coating repair process: Sanding down to bare metal. Courtesy of Stuart Dean.
AAMA
Coating thickness (ASTM )
0.02'0.3 in.
Chromium content in conversion coat (ASTM D)
' 40 mg/ft2
Curing temperature
500˚F
Chemical resistance (ASTM D543)
Excellent
Abrasion resistance (ASTM D)
Excellent
Pencil hardness (ASTM D)
F, minimum
Tensile strength at break (ASTM D638)
psi
Coefficient of friction (ASMT D)
0.4 static, 0.3 dynamic
Dielectric strength (ASTM D149)
260 V per mil
Hardness (ASMT D676)
80 (shore D)
Common warranty duration(s)
10'20 years standard
Table 2. Polyvinylidene fluoride coating statistics and specifications
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When doing a complete recoat, all perimeter sealants and any exposed sealants (that is, any sealants in contact with the metal) need to be fully removed prior to recoating and replaced afterward. Partial recoats usually requires application of a clear coat, which may or may not be required in a total recoating protocol.
The first step is to sand all affected surfaces down to the bare metal (Fig. 12). The next step is to remove corrosion-causing chlorides from the aluminum by chemically treating it and microblasting affected areas to remove oxidation cells (Fig. 13).
Next, the bare metal is treated with an acid etching chemical and the corrosion-resistant chromium-based primer is applied to the bare metal. Following that, an epoxy primer is applied to the entire metal unit and sanded down lightly in preparation for the top coat (Fig. 14).
PVDF COATINGS VERSUS ANODIZED ALUMINUM: ARE
PVDF COATINGS STILL BETTER?
While the industry is not ready to publicly acknowledge this problem, there is a clearly documented issue with premature PVDF coating failures. However, there are ways to mitigate premature failure while the industry collectively figures out how to proceed.
Despite the increase of failures, PVDF coatings are still the best choice for most projects (assuming they are properly specified and tested). Here is why PVDF coatings are still a better choice for most projects than anodized aluminum:
' Durability and longevity: The oxidizing layer of anodized aluminum is typically only 0.07 mil and is susceptible to corrosion, particularly in coastal climates. Thicker, more customized coatings cost more. PVDF coatings (when used with a chrome-based conversion coating and properly applied) will outlast anodized aluminum.
' Warranty considerations: Anodized aluminum extrusions are typically under warranty for 5'10 years, depending on a variety of factors. PVDF coatings commonly come with a 10- to 20-year warranty.
' Cost: The initial cost of anodized aluminum can be lower than PVDF coating. However, when factoring in eventual replacement costs (because field repair is not an option), anodized finishes cost more over time. Many manufacturers have also adopted PVDF coatings as their standard of care and most architects specify them. Anodized coatings are inferior on most scales, and can end up costing more than PVDF coatings.
' Aesthetics/color availability: Anodized aluminum is available in limited color options: bronze, clear, black, and champagne. PVDF coatings are available in an array of colors and can be custom made to match virtually any building exterior.
When PVDF coatings are properly specified to include a chrome-based conversion coating, PVDF coating can still last the lifespan of a new building, even in coastal environments. While the ASTM committee is still in deliberation, we fully expect the standard will be revised to once again mandate this practice. However, proper verification testing will still be critical.
Figure 13. The coating repair process: Microblasting
to remove oxidation. Courtesy of Stuart Dean.
Figure 14. The coating repair process: Top coat application. Courtesy of Stuart Dean.
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REFERENCES
1. Aluminum Development Association, 'The Properties of Aluminum and Its Alloys,' Information Bulletin no. 2 (London, UK: Aluminum Development Association, ), 11.
2. J. D. Minford, Handbook of Aluminum Bonding Technology and Data (New York: Marcel Dekker, ), 84 and 95.
3. American Architectural Manufacturers Association (AAMA), Voluntary Specification for Anodized Architectural Aluminum, AAMA 611. Schaumburg, IL: AAMA.
4. ASTM Subcommittee B08.07, Standard Specification for Anodic Oxide Coatings on Aluminum, ASTM B580-79(). West Conshohocken, PA: ASTM International, .
5. Apex Aluminum Extrusions ' 5 Year Limited Warranty
6. Linetec, 'Sample 5 Year Limited Warranty: Anodizing,' https://linetec.com/wp-content/uploads//04/Sample_Anodize-5_New.pdf.
7. Can Art Aluminum Anodizing, 'Limited Warranty for Architectural Class 1 and Class II Anodizing of Aluminum,' http://www.canart.com/pdf/warranty.pdf.
8. AAMA, Voluntary Specification, Performance Requirements and Test Procedures for Superior Performing Organic Coatings on Aluminum Extrusions and Panels, AAMA . Schaumburg, IL: AAMA.
9. AAMA, Voluntary Specification, Performance Requirements and Test Procedures for High Performance Organic Coatings on Aluminum Extrusions and Panels, AAMA . Schaumburg, IL: AAMA.
10. Fonnov Aluminium, '2-Coat and 3-Coat PVDF Coating Process on Aluminium,' https://www.fonnovaluminium.com/pvdf-coating-on-aluminum.html.
11. AAMA, Voluntary Specification for High Performance Organic Coatings on Architectural Extrusions and Panels, AAMA 605.2. Schaumburg, IL: AAMA.
12. ASTM Subcommittee D20.15, Standard Specification for Unmodified Poly(Vinylidene Fluoride) (PVDF) Molding Extrusion and Coating Materials, ASTM D-18a. West Conshohocken, PA: ASTM International, .
13. ASTM Subcommittee D01.53, Standard Practice for Determination of Chromium Treatment Weight on Metal Substrates by X-Ray Fluorescence, ASTM D. West Conshohocken, PA: ASTM International.

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What You Need To Know About PVDF Coatings For Architectural Aluminium

March 11,

There are many coatings that can be applied to aluminium to achieve several beneficial effects, including enhancing durability and improving visual appeal. However, before you decide what kind of coating you want your aluminium to have, one of the most common for architectural and low maintenance coatings is PVDF.

What exactly is a PVDF coating? How is it applied? Why should you choose this coating over other alternatives? 

Read on to learn even more about this type of coating and why it may be perfect for your building's facade.

What Are PVDF Coatings?

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PVDF coatings, or polyvinylidene fluoride coatings, are resin-based coatings that can be applied to aluminium. It is part of the Fluorocarbon family of plastics, which forms bonds that are extremely chemically and thermally stable. It has many practical and visual advantages that can make your architectural aluminium more functional and aesthetically pleasing. It is commonly used for commercial buildings and residential dwellings. 

PVDF coatings are often applied using a spray gun in the following steps:

1. The Aluminium Surface Is Prepared. Before any coating is applied, the aluminium must be prepared. This means it should be cleaned and degreased, and any rust should be removed. If the aluminium is dirty or not prepared properly, the coating may not hold as it should and it might not have the desired effects. Certain high-quality PVDF coatings also need a chrome-based conversion coating to be put on the aluminium before a primer is applied.

Are you interested in learning more about custom pvdf coating on aluminium company? Contact us today to secure an expert consultation!

2. A Primer Is Applied. Next, a primer is used on the aluminium to stabilise it and prepare it for the PVDF coating. 

3. The Top Coat Is Applied. The top coat is applied to the aluminium. This top coat can include colour particles to improve the aesthetic appeal of the aluminium. This coating, which is the thickest coating in this process, provides damage and abrasion resistance. This top coat must be adequately cured after it's applied. Once it is, the next step can commence.

4. The Clear Coating Is Applied. In most coating processes, the final step is to apply the clear coating to the aluminium. This clear coat gives the metal an extra layer of defence from the outside elements while letting the top coat's colour show through. This clear coat, in addition to providing more protection to the material itself, also protects the colour and prevents it from easily coming off.

Why Should I Choose PVDF Coated Aluminium For My Building's Facade?

You may be asking, 'why should I choose PVDF-coated aluminium over other alternatives?' You should know that this coating provides your aluminium, and thus your facade, with many fantastic benefits. 

These include:

• It's More Environmentally Friendly. PVDF coatings are considered more eco-friendly than many other alternatives because they do not contain volatile organic compounds. If you're concerned about your environmental impact, this may be the right choice for you. 
• It Offers Sunlight Resistance. Too much New Zealand UV rays can cause certain coatings to become faded or damaged. PVDF coating is resistant to UV rays and keeps your aluminium looking brand new for many years.
• It Offers Damage Resistance. PVDF coatings offer damage resistance to a wide variety of factors. These coatings can protect against weather, general wear, abrasion, corrosion and more. Overall, this extra protection can help your aluminium facade stay appealing for much longer.
• It Requires Minimal Maintenance. Along with being long-lasting, PVDF-coated aluminium requires very minimal maintenance. So, you can enjoy its benefits without worrying about complex and continual washing and care. 

What's The Difference Between PVDF And Powder Coatings?

Another option you can choose is powder-coated aluminium, which is different from PVDF coatings in a few ways. You should know that PVDF coatings are different from powder coatings in these ways:

• PVDF Coatings Use Fluid Paint, Powder Coatings Use Powder.
• PVDF Coatings Are Thinner. 
• PVDF Coatings Can Be Cured At Room Temperature, Rather Than Being Baked.
• PVDF Coatings Are Sunlight Resistant And Will Not Fade Over Time. 
• PVDF Coatings Are More Expensive When Compared To Typical Powder Coatings.

Overall, if you want a coating that'll provide you with high durability and beautiful colours and are willing to pay a bit more for great quality, PVDF coatings may be the perfect choice for you.

Where Can I Learn More About My Architectural Aluminium Options In New Zealand?

The type of aluminium you choose for your building's facade is an important choice because it'll affect the visual appeal of your facade while strongly affecting how durable and long-lasting it is. At Paneltec, we're here to help you make the best choice possible. 

We have a great range of products that you can browse through. We know that every building is unique, and we'd love to help you find the perfect product for yours.

Would you like to know more about your options? Call us at 09 439 or visit our contact page to get in touch with our team.

Ensure your building's facade is strong, long-lasting and very beautiful with us at Paneltec.

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