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High-Profile Roofing: Advancement in Fluropolymer Top-Finishes for Roofing Membranes

May 15, 2015

Technology advancements in
industrial coated fabrics are
leading the way for new opportunities
in the single-ply membrane
market. Factory-applied
high-performance coatings,
combined with gravure printing technologies,
are breaking typical roofing paradigms
and offering architects solutions to previously
unmet customer needs. This article
will discuss these advancements and their
transition into today’s single-ply roofing
market.
THE PREMISE
In the 1970s, the roofing industry borrowed
reinforcement technology from the
polymer-coated architectural fabric market
to lay the foundation for most of today’s
single-ply roofing membranes. These two
markets are merging again. As these platforms
merge, additional advancements are
happening on both fronts.
Since their conception, thermoplastic
roofing membranes, initially designed for
low-slope roofing applications, have been
used for high-profile, highly visible steepslope
roofing solutions. It was a natural evolution.
The versatility of these membranes,
combined with their exceptional weathering
characteristics and watertight integrity,
allowed designers and architects to express
their creativity in new ways.
Monolithic coverings brought dynamic
shape and aesthetics to the structures that
rigid materials such as stone and metal or
even shingles, for that matter, could not
accommodate. It soon became clear that
architects were not just designing buildings;
they were creating art (Photo 2).
The single-ply membranes did an excellent
job from an initial installation perspective;
but dirt pickup, which had nothing to
do with the overall performance of the products,
soon diminished the aesthetic value of
J u l y 2 0 1 5 I n t e r f a c e • 9
HIGH-PROFILE
ROOFING:
Photo 1 – Beth El Temple, St. Petersburg, Florida. Kynar-coated single-ply.
Photo 2 – The Ascent at Roebling’s Bridge, Covington, Kentucky.
By Jerry Beall
Advancements in
Fluoropolymer
Top-Finishes for
Roofing Membranes
the structure and the overall appeal of the
membranes. Even though the roofs could be
cleaned and restored to their as-new appearance,
the expense was not something the
owners anticipated or appreciated.
In spite of all the positive attributes
afforded these single-ply materials, there
was something lacking. The materials themselves
were not specifically designed to provide
the optimum solution to the designers’
overall expectations.
A study of the “high profile” market’s
needs revealed that there were some significant
customer satisfaction gaps when
measured against current product offerings.
Sure, watertight performance, attractive warranties, and overall ease
of installation were givens. But over time, fading colors and dirt pickup
diminished the aesthetics of the structures’ as-new appearance
(Photos 3 and 4).
What was really needed was an architectural roofing solution
specifically engineered to address the long-term need to maintain aesthetics
without sacrificing the inherent performance attributes of these
materials. To determine the optimum solution, a thorough analysis of
the customer satisfaction gap was in order.
A dynamic study was undertaken that included extensive interviews
and opinion surveys of architects, roof consultants, and roofing
contractors. The gap is a measure of their satisfaction with currently
available membrane solutions and characteristics compared with their
preferred or optimum desires (Figure 1):
• Color that doesn’t fade
• Membranes that stay clean
• Patterns to create depth and break up color monotony
• A broad range of color options
• Warranties
1 0 • I n t e r f a c e J u l y 2 0 1 5
Photo 3 –
University
of Florida
O’Connell Center,
September 2005.
Photo 4 –
University of
Florida, O’Connell
Center, May
2008, after
cleaning. The
white structure
below the roof
area is a Tefloncoated
fiberglass.
Figure 1 – The gap is a measure of building professionals’ satisfaction
with currently available membrane solutions and characteristics
compared with their preferred or optimum desires.
The solutions also had to meet a host
of standard external requirements for fire,
wind, and general weathering performance.
So the ultimate solution
could not overlook
the many givens
required for commercial
roofing in general.
These external
requirements can
be summed up by
just saying Factory
Mutual (FM) and UL
approvals.
While this challenge
may have been
new to commercial
membrane roofing, it
had been addressed
long ago in the architectural
fabric structure
market. In these
markets, the vinyl
membrane is the roof,
and initial and longterm
aesthetic performance
is critical to
the satisfaction of the
customer.
And, similar to today’s highly visible
commercial roofing, these single-ply materials
offered an endless opportunity for architects
to express themselves in shape and
color; and, just like commercial high-profile
roofing, maintaining aesthetics over time is
an important consideration in the selection
of materials.
For their ultimate solution, the architectural
fabric industry borrowed a page from
the metal roofing industry. By using a fluoropolymer
film or top finish applied during
the manufacturing process, the architectural
fabric industry was able to offer the ultimate
solution to the aesthetic expectations
of their customers (Photo 5).
These coatings and/or top-finishes protected
the metal from corrosion as well as
promoted unlimited color options with minimal
dirt pickup. Hence, a top finish (factory-
applied coating) was applied to protect
vinyl membranes from ultraviolet radiation
(UV) and its effects. The top-finish could
restrict plasticizer migration, prevent colors
from fading, and repel dirt. Early top-finish
solutions utilized acrylics, which offered a
solution—albeit temporary at best. Acrylic
resins contain esters
and incorporate other
functional groups
that are susceptible
to photochemical degradation
and hydrolysis,
both of which
are prominent during
typical environmental
exposure. These conditions
contribute to
the ultimate breakdown
of the protective
acrylic layer.
Eventually, degradation
of the top finish
left the vinyl exposed
to the effects of UV.
Plasticizers would
begin to migrate, colors would fade, and
dirt would collect on the structures.
COATING FUNDAMENTALS
The performance of many materials can
be enhanced with an exterior barrier that
preserves the inherent properties of the
base material. Paint, which is essentially
a coating, has been used for this purpose
for hundreds of years. This technology
has advanced to include some pretty hightech
solutions for the construction market,
whether field-applied (Photo 6) or in the form
of factory prefinished materials (Photo 7).
J u l y 2 0 1 5 I n t e r f a c e • 1 1
Photo 5 – Fluoropolymers were metal
roofing’s solution for corrosion and
aesthetics.
Photo 7 – Factory-applied top finish.
Photo 6 – Fieldapplied
coating.
In general, coatings—whether factoryor
field-applied—have the same functional
requirements. Yet in certain cases, such as
architectural fabrics, coatings can be used
to protect the primary waterproofing, coatings,
and/or polymers. These factory-applied
coatings are often referred to as topfinishes.
Paints or coatings in this context are
generally classified into two categories:
water-based and solvent-based. Solventbased
coatings use a carrier consisting of
volatile organic compounds (VOCs). VOCs
can cause smog, ozone pollution, and indoor
air quality problems. Newer formulations
contain more solids and less solvent or environmentally
friendly solvents such as water.
Additives may be used in small amounts
in comparison to the main ingredients. They
include flatting agents, rheology modifiers,
wetting agents, and curing agents.
Binders allow for curing of the coating,
which increases physical strength and
chemical resistance of the coating film.
The binder is the primary source for the
coating’s durability and physical properties.
Binders differ in their ability to withstand
UV exposure. The type of binder used is one
of the most significant criteria in choosing
an exterior coating.
Acrylics are one of the most common
binders used for coatings. For field-applied
roof coatings, we see a lot of acrylics (and
now, urethane) being used to coat not only
metal, but single-plies. We also have new
fluoropolymers blended with acrylics entering
the roofing market.
The better the binder or “resin,” the
better the coating or top finish will perform.
Solvents are chosen based on system
compatibility and evaporation rate.
Environmental concerns have pushed the
technology toward water-based materials
that now perform as well if not better than
solvent-based ones.
FLUOROPOLYMERS
Fluoropolymers share the properties
of fluorocarbons
in that they promote
a high surface
tension phenomenon
that contributes
to their nonstick
and frictionreducing
properties.
In addition, they
are stable due to
the strength of their
multiple carbonfluorine
bonds.
F l u o r o p o l y m e r s
may be mechanically
characterized
as thermosets or
t h e r m o p l a s t i c s .
Fluoropolymers can
be homopolymers
or copolymers.
In 1938, polytetrafluoroethylene
(PTFE) was discovered
by accident by a recently hired DuPont
chemist, Roy J. Plunkett (Figure 2). While
working with tetrafluoroethylene gas, he
noticed missing weight. While scraping
down his container, he found white flakes of
a new-to-the-world polymer. Testing showed
that the substance was resistant to corrosion
from most substances and had better
high-temperature stability than any other
plastic known at the time. By early 1941,
a crash program was making commercial
quantities of this unique plastic: Teflon.1
See Photo 8.
Fluoropolymers make excellent protective
coatings because of their inherent
chemical and UV resistance. In many cases,
they are the preferred choice for protective
coatings.
The carbon-fluorine bond is the key to
the thermal, chemical, and UV-resistance
properties of all fluoropolymers. The number
of fluorine atoms present in a given
fluoropolymer has a direct bearing on its
performance.
The unique combination of properties of
fluoropolymers is attributed to two intrinsic
characteristics of fluorine atoms—extremely
high electro-negativity and small atomic
radius. The atomic structure of fluorine
gives rise to some of the strongest chemical
bonds known.
As if the roofing industry doesn’t have
enough acronyms, here are a few more for
you.
Polytetrafluoroethylene (PTFE), polyvinyl
fluoride (PVF), and polyvinylidene fluo-
1 2 • I n t e r f a c e J u l y 2 0 1 5
Photo 8 – Teflon is the only known surface to which a gecko cannot
stick.
Figure 2 – Polytetrafluoretheylene
(Teflon®).
PTFE (Teflon)
• Third-lowest coefficient of friction known to any solid
• The only known surface to which a gecko cannot stick
ride (PVDF) are the three
most commonly used
fluoropolymers today.
Although best known
for their nonstick characteristics,
they are also
extremely durable materials.
In many instances,
these are very thin films,
measuring no more than a
few microns. PTFE (Teflon)
is most recognized as a
nonstick coating for cookware.
It is very nonreactive—
partly because of the
strength of the carbonfluorine
bond. PTFE is
often used in containers
and pipe work for reactive
and corrosive chemicals.
PTFE-coated fiberglass is a popular noncombustible,
coated fabric used in the
architectural structure market. This is
especially true in the U.S., as the structure
must pass a similar battery of fire tests
to that required for roofing materials: the
burning brand test.
PVF (Tedlar)2 is the predecessor to PVDF
in architectural fabric coatings and has
performed in the architectural market for
over 30 years (Photo 9). This film has been
used extensively in the construction market
on vinyl siding, architectural shingles, and
membrane structures.
PVF resin is structurally similar to PVC
resin in that it has low permeability for
vapors, burns very slowly, exhibits excellent
resistance to weathering and staining,
and is resistant to most chemicals except
ketones and esters.
Low water permeation, high-UV resistance,
color stability, and good chemical
resistance are properties of this 1-mil film
that provide a high-performance, long-term,
durable surface in harsh environments.
Until recently, this product was the best
solution for long-term performance in the
architectural fabric market. With the rise
in usage of PVF in photovoltaic cells, a new
film was needed in the architectural market
to act as an alternative and provide yet
another superior alternative to acrylics.
PVDF (Kynar)3 is a highly nonreactive
and pure thermoplastic fluoropolymer produced
by the polymerization of vinylidene
difluoride. PVDF is a specialty plastic material
in the fluoropolymer family; it is used
generally in applications requiring the highest
purity, strength, and resistance to solvents,
acids, bases, and heat and low-smoke
generation during a fire event. Compared to
other fluoropolymers, it has an easier melt
process because of its relatively low melting
point of around 350°F (177°C).
It also has a low density and low cost
compared to other fluoropolymers. PVDF is
available as piping products, sheet, tubing,
films, plate, and an insulator for premium
wire. It can be injected, molded, or welded,
and is commonly used in the chemical,
semiconductor, medical, and defense industries,
as well as in lithium ion batteries. It
is also available as cross-linked closed-cell
J u l y 2 0 1 5 I n t e r f a c e • 1 3
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Photo 9 – Tedlar-coated polyester on an aquatic center.
foam, used increasingly in aviation and
aerospace applications.
Fortunately, and unlike the other two
fluoropolymers discussed, PVDF is also
used as the principal ingredient of high-end
paints for metals (Photo 10). These PVDF
paints have extremely good gloss and color
retention and are used on many prominent
buildings around the world, as well as on
commercial and residential metal roofing.
The most significant property of PVDFbased
coatings is their outstanding exterior
durability. The exceptional weatherability
is a result of the strength of the carbonfluorine
bond, which is one of the strongest
chemical bonds known. The bond strength
provides a chemically inert coating with
complete resistance to UV light exposure.
UV radiation is one of the major causes of
deterioration of a coating exposed to the
atmosphere.
Commercial coatings can fade over time.
PVDF offers unique weathering properties.
As it is invisible to UV, it holds up to the
sun’s energy and doesn’t break down. It also
allows the use of high-performance metal
oxide pigments. These pigments resist fading
much better than conventional organic
pigments.
MERGING TECHNOLOGIES
The transfer of architectural fabric
top-finish technology to roofing has had
its challenges. From a purely technical
perspective, creating the fabric was a fairly
simple transition.
The greater challenge
was turning the Kynarcoated
fabric into a reliable
and easy-to-install
roofing system.
It has become the
general rule of roofing
to place a heavy emphasis
on aesthetics, but
the expectations with
Kynar-coated membrane
are reaching new
heights (Photo 11). This
challenge is magnified
by the fact that the factory-
coated top-finish is
nonweldable. However,
the selvedge edge or
coating miss along the
edge of the membrane will facilitate the vast
majority of field welding.
There are numerous advantages of having
a factory-applied finish as opposed to a
field-applied finish (Photo 12).
This is a unique technological advancement
in the art and applied engineering of
coated fabrics. The application of the top
finish involves more than just applying a
layer of coating. It is a multi-step process to
1 4 • I n t e r f a c e J u l y 2 0 1 5
Photo 10 – Field-testing and weathering of PVDF.
Photo 12 – Working with a
preprinted metal profile illusion on a
fluoropolymer roofing membrane.
Photo 11 – Plainview Elementary School,
Plainview, Texas, with its “Dazzle Blue”
Kynar roofing system.
ensure optimum adhesion of the finish to
the vinyl membrane.
Roofing membranes with a fluoropolymer
top finish offer a broad spectrum of
color options that do not fade, and the
inherent low coefficient of friction reduces
dirt accumulation on the surface of the
membrane.
The transfer of this top-finish technology
to roofing permits the membrane to have
the advantage of thermoplastic seams and a
highly durable yet nonthermoplastic finish.
Today’s emphasis on energy savings
through highly reflective roofing makes a
premiere membrane with top-finish very
appealing. Imagine a white roof that stays
clean or a blue roofing membrane that
doesn’t fade and also meets 20-year performance
expectations.
Fluoropolymer-coated roofing membranes
require forethought on the part of the
craftsman during layout of the membrane
and assembly. Joining the membrane at
flashing and roll ends or anyplace else that
the fluoropolymer would impede welding is
pretty simple, but requires either a removal
process for the fluoropolymer or an underlying
uncoated base membrane. A masking
process is used along with cleaning the fluoropolymer
with methyl ethyl ketone (MEK)
to ensure straight edge laps. PVDF (with
the exception of ketones) is very chemicalresistant.
Care must be exercised to avoid splashing
or spilling the MEK on the unmasked
portion of the membrane, as it will damage
the fluoropolymer top-finish.
This process is applied to any seam that
needs to be made within the fluoropolymer
top finish of the membrane, including flashing
and repairs.
Once the welding techniques are mastered
(Photo 13), the other challenge is hid-
J u l y 2 0 1 5 I n t e r f a c e • 1 5
Photo 13 – Fluoropolymer removed and ready to weld.
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ing the substrate and preventing it from
telegraphing through the adhered membrane.
The most likely method to accomplish
this is to mechanically fasten the insulation
composite as required and bond a coverboard
in urethane foam adhesive to the insulation.
However, this, too can have its challenges.
The incorporation of a “fleece” on the
back of the membrane helps hide substrate
imperfections.
For the job shown in Photo 14, the
contractor had to take additional steps to
tape and grout the joints in the gypsum
coverboard to minimize any telegraphing in
order to please the architect’s demand for
impeccable aesthetics.
ADVANCING TECHNOLOGY
Breaking up the monotony of a highprofile
roof is a desired attribute for a
single-ply roofing membrane, according to
the architects interviewed. Technology has
advanced to the point that printed patterns
and/or illusions using fluoropolymer coatings
are now possible.
This is a big step up from the current
illusions available in the
market that simulate
shingles or stone and
are typically printed with
acrylics.
The type and choice of
pattern will determine the
final aesthetics. The patterns
can be fairly intricate,
such as the ones
shown in Photo 15, or
larger in their repeat pattern
to create some pretty
astounding visuals.
Custom designs will
open the door for unlimited
design options; and,
based upon initial studies,
the possibilities for
artistic expression are
endless.
Thermoplastic single-ply roofing has
been improving and advancing since its
initial conception in the 1960s. As customer
expectations expand, fluoropolymers are
creating unique opportunities to meet these
expectations, as well as interject new creativity
into the architectural design process.
REFERENCES
Robert A. Lease, “Creating Coatings
for Better Buildings,” Elf Atrochem
North America, Inc.
Sue Uhler, “Use of Kynar as a Top Finish
in Architectural Fabrics,” Seaman
Corporation.
Kurt Wood, Akira Tamaka, Min Zhey,
and Dana Garcia, “70% PVDF
Coatings for Highly Weatherable
Architectural Coatings,” Atrifina
Chemicals.
“Selecting a Resin-Based Coating for
Metal,” AIA Course No. AK0901,
Arkema Inc.
“Use of Water-Based PVDF Coatings for
Sustainable Design,” AIA Course No.
AK0902, Arkema Inc.
FOOTNOTES
1. Teflon is a registered trademark of
DuPont.
2. Tedlar is a registered trademark of
DuPont.
3. Kynar is a registered trademark of
Arkema Inc.
1 6 • I n t e r f a c e J u l y 2 0 1 5
Jerry Beall’s roofing
industry career
spans 40 years,
stemming from a
10-year stint as
a journeyman in
Roofers Local #88.
He joined Seaman
Corporation in
1984 and spent
five years as
FiberTite’s senior
technical service
representative. During a three-year absence
from Seaman, he worked with a Florida
roofing contractor and then returned in 1992
as a FiberTite® Roofing Systems technical
manager. In 2000, he became national sales
and technical manager for FiberTite. Four
years later, Beall assumed his current role
as FiberTite technical and product specialist.
Jerry Beall
Photo 14 – Substrate preparation and grouting of the underlayment on Beth El Temple,
shown in Photo 1.
Photo 15 – Patterns allow for unlimited architectural expression,
such as on the roof of this airport.