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That Old Black Magic: Fluid-Applied, Polymer-Modified Rubberized Asphalt

February 15, 2000

Commonly referred to as “hot rubberized
asphalt,” fluid-applied, polymer-modified
asphalt bitumen is also known by a
number of monikers, including fluid-applied,
hot-melt waterproofing; fluid-applied,
monolithic membrane; rubberized asphalt
membrane; and different combinations of
these descriptive words, as well as various
The two primary components of early
polymer-modified rubberized asphalt—
unoxidized asphalt flux and styrene butadiene
rubber (SBR, a synthetic rubber)—were
considered to be incompatible with each
other prior to innovative molecular engineering
by a number of early pioneers.
When asphalt flux and synthetic rubber
are put in intimate contact, the light ends
of the asphalt flux molecularly migrate into
the rubber, causing it to swell and disfigure
to a large, variable multitude of its original
size, a classic incompatible response, as the
minor constituent—rubber—becomes the
major constituent of the mix.
The first usable rubberized asphalt
material was developed in the early 1950s
and reported as such in “Highway Research
Report No. 25,” published by the University
of Michigan in 1955, with a second paper
published in 1957. The next generation of
rubber polymer, styrene butadiene styrene
(SBS), was invented in the U.S. in the late
1960s at Shell’s West Hollow Research
Center in Texas. Nevertheless, most development
and material engineering refinements
were made in Europe by, among others,
Shell’s French subsidiary, Shell France
Bitumen Corp., starting around 1972.
As product development continued in
the 1950s, chemical engineers learned how
to use high-shear mixers in such a manner
that the absorption and expansion of
the rubber component molecules could be
engineered and controlled, resulting in an
end product that was a stable, rubber-like,
elastomeric-thermoplastic asphaltic material.
At that time, the chemical engineers
imagined an unlimited number of applications
in highway construction—the 800-
pound gorilla of asphalt consumption that
it still is today. Subsequently, their vision
grew to include roofing, and their primary
focus became preformed SBS sheet roofing.
SBS modified-bitumen sheet roofing was
introduced into both the American and
Canadian markets around 1977. Fluidapplied
waterproofing incorporating SBS
was not given much thought at that time.
n o v e m b e r 2 0 1 3 I n t e r f a c e • 7
Photo 1 – Fluid material withdrawn from double-jacketed melter.
Part I of “That Old Black Magic” was published in the February 2000 edition of Interface.
Backtracking a bit, sometime around
1963, Uniroyal Ltd. (then the Canadian
subsidiary of Uniroyal, Inc.) started to use
an SBR-asphalt compound experimentally
on some of its own roofs. After a few years
of observation, Uniroyal Ltd. started marketing
the material in Canada as a fluidapplied
waterproofing material suitable for
One of the unique properties of rubberized
asphalt is the amazing coldtemperature
flexibility of the material, typically
-20°F (-29°C) and even lower, when
compared with oxidized roofing asphalt,
which commonly has a glass transition temperature
of 38° to 40°F (3 to 4°C).
Not surprisingly, the hot-rubberized
market found reasonable acceptance in the
cold Canadian climates. Uniroyal Canada,
Ltd. soon had competition from Flintkote of
Canada. By the 1970s, there were at least
five more significant suppliers of rubberized
asphalt in Canada: Bakelite Thermoset;
Bitumar; PennKote Ltd.; Tremco Canada,
Ltd.; and Koch Materials Co. At least three
of the companies (most noticeably, Uniroyal,
Ltd.) also sold nominal amounts of rubberized
asphalt material in the U.S. market.
Rubberized asphalt did not start to
develop any significant market share or
market acceptance in the U.S. until the
late 1970s. By the early 1980s, there were
four notable rubberized asphalt suppliers
in the U.S. market, enjoying a nominal but
expanding market share of the commercial
roofing and waterproofing industry,
with most of the rubberized asphalt being
imported from Canadian blending plants.
Today there are 12 suppliers of rubberized
asphalt in the American market and
several more serving the Canadian market.
More than half of the polymer-modified
rubberized asphalt used in the U.S. today is
still imported from Canada. The value of the
increased competition to the industry stakeholders
is debatable but certainly follows
the pattern of a normal product life cycle
and the basic laws of economics.
AN eNgINeeRed mATeRIAl
The chemical makeup of polymermodified
rubberized asphalt can vary significantly
from producer to producer. The
variables include:
• The compatibility of the raw, unoxidized
asphalt flux with the polymerization
• The specific polymer used
• The amount of polymer used
• The type and amount of filler material
(if any)
• Any other additives employed to
impart particular properties or characteristics
It is widely estimated that only 50-60%
of all asphalt flux is compatible with the
polymerization process; and within the compatible
fluxes, the degree of compatibility
ranges from slightly compatible “harder”
asphalts to highly compatible “softer”
asphalts. The highly compatible
asphalts constitute
about 10% of all asphalt
and tend to be more
expensive, originating from
“sweet crude” petroleum.
Only one producer is
known to have used oxidized
“blown” ASTM D312–
type roofing asphalt to
make a rubberized asphalt.
The roofing asphalt oxidiz-
8 • I n t e r f a c e n o v e m b e r 2 0 1 3
Photo 2 – Fluid material being spread with a squeegee.
Photos 3A-3C — Installing and overcoating polyester
ing process is essentially accelerated aging
of asphalt flux for roofing applications by
raising its softening point with steam and
heat so it does not flow off roofs as raw
asphalt flux would. Using unblown asphalt
flux to make rubberized asphalt theoretically
provides a longer lifespan for the material
and, compared with oxidized roofing asphalt
flux, is significantly more compatible with
the polymerization process.
The polymer component is at least equally
as important as the flux compatibility. In
the early days of rubberized asphalt, there
was SBR, the first synthetic rubber polymer
derived from crude oil. SBR is an engineered
chain of molecules that can be manipulated
in many different configurations that impart
different properties. When the polymer is
mixed in sufficient quantity with compatible
asphalt flux in a high-shear mixer, a polymerized
rubber network is created. During the
process, the rubber polymer components
absorb the light ends of the asphalt, swelling
or expanding in volume by more than
800% and creating the polymerized network
of rubberized bitumen. The overall volume
of the composite material does not change;
but in absorbing the light fractions
of the asphalt, the minor
constituent rubber polymer
becomes the major constituent
with a phase change. Under a
microscope, a cross section of
this material would resemble
a sponge, with the sponge’s
air spaces filled with asphaltic
fractions and the structure
of the sponge represented by
the tumescent rubber polymer
network that has swelled up
after absorbing the light ends.
A simple visualization example
would be imagining 10% polymer
mixed with 90% bitumen,
resulting in a 80-90% rubber
network with 10-20% bitumen
As previously mentioned,
in the early 1970s, Shell Oil’s
Kraton® Group introduced SBS
polymer to Shell France
Bitumen Corp., which, in turn,
n o v e m b e r 2 0 1 3 I n t e r f a c e • 9
Photo 4 – Column detailing.
working with the European roofing industry,
produced an entirely new class of roofing
materials: SBS “mod-bit” sheet roll roofing.
Subsequently, most manufacturers of rubberized
asphalt roll roofing slowly replaced
SBR polymer with SBS. Rather than offering
the SBR “chain” of styrene-butadiene rubber
configurations, SBS provides a block
formation of styrene-butadiene-styrene molecules
that can also be engineered and
manipulated into a wider variety of different
configurations than SBR. The new SBS
polymer material offered greater strength,
improved elastomeric properties, and easier
material compounding to reach a polymer
phase than SBR. Not surprisingly, SBS also
came with some increased polymer costs.
Shell’s Kraton® Group also introduced
styrene ethylene butylene styrene (SEBS)
in the late ’70s, billing it as the next generation
of rubber polymer suitable for mixing
with asphalt. The product provided greater
resistance to manufacturing-process heat
damage and also offered high resistance to
ultraviolet degradation, two areas to which
SBS is less resistant. Given the significantly
higher cost of the SEBS polymer (about
three times as much as SBS), it never
found its way into the rubberized asphalt
market. It has, however, developed a niche
market as an upgraded polymer-modified
mopping bitumen in elastomeric built-up
systems and as an SBS-modified-bitumen
sheet adhesive providing 100% modified
membrane assemblies. Possibly incompatible
oxidized Type-III asphalt—a condition
that can be problematic in the top ply of a
multi-ply system due to its difference in performance
at varying temperatures—is thus
eliminated from such assemblies.
Worth noting is another recent market
digression by one manufacturer of rubberized
asphalt: the elimination of all polymers
from its product, replacing them with cryogenically
ground crumb rubber derived from
automobile tires. This concept is ecologically
very beneficial. The cryogenic crumb
imparts a number of desirable rubberlike
properties; however, there is no polymerization
or a cross-linking polymer network—
only swollen rubber particulates suspended
in asphalt. Within the industry, this type of
product is referred to as “asphalt-rubber,”
as distinguished from (polymer-modified)
rubberized asphalt. The loss of the polymer
network really makes it an entirely
different material from a polymer-modified
rubberized asphalt, and it is a material
that does not come close to meeting CAN/
CGSB-37.51-M90 specifications, the only
recognized standard of quality for polymermodified
rubberized asphalt as cited in
ASTM D6622. “Asphalt-rubber” has found
wide acceptance as a low-cost highway
crack sealant; however, it has not been used
very much for waterproofing or roofing.
After considering rubberized asphalt’s
two primary components of bitumen and
polymer, the next element in rubberized
asphalt is filler materials. It seems each
supplier has its own ideas of the best mix of
filler material. At least one uses clay, several
use calcium carbonate or crushed limestone
rock, several use talc and slag, at least one
uses black marble dust, one uses slate
dust, many use recycled tire crumb rubber
as a second filler material, and at least one
doesn’t use any filler at all.
The primary technical value of filler
material in rubberized asphalt is that it
increases rubberized asphalt’s viscosity,
resulting in a thickness build during application
that is not obtained without the
filler. The thicker viscosity results in thicker
buildup of membrane during application,
which results in superior crack-bridging
and self-healing properties, increasing
the abuse resistance of the membrane
to mechanical damage and construction
1 0 • I n t e r f a c e n o v e m b e r 2 0 1 3
Photo 5 – Completed view of column detailing at Soldier Field.
Photo 6 – Installing protection course.
activity. Fillers can also improve uniformity,
reduce flow characteristics, and some
can even impart additional strength to the
material. The ecological benefit of using
tire crumb as a second filler is self-evident.
Not as evident is the fact that the right
size of crumb rubber can act as little “ball
bearings,” helping to regulate application
thickness. Since most fillers are inert and
the filler particulates are coated with the
rubberized asphalt during the mixing process,
the net difference between one inert
filler and another is not considered significant.
Also, fillers cost less than asphalt flux
and a lot less than polymer. The value of not
using any filler (all other things being equal)
is that the rubberized asphalt material has
increased tensile strength and increased
cohesive strength, and it will be installed in
thinner layers, which may be desirable in
certain applications.
While these two to four components are
blended with the high-shear mixer, there are
a number of proprietary additives that can be
employed to compensate for lower asphaltflux
compatibility, change the finished material’s
surface tension, increase the material’s
adhesion, make the material harder or softer,
change softening points, increase fire resistance,
and other modifications that might be
desired or dictated by quality assurance (QA)
testing before packaging.
Most manufacturers will have a battery
of quality control tests run on the
raw-asphalt flux coming into their plants,
as well as testing of the completed mixed
material in on-site labs before the material
is packaged. In the event the material mix
does not meet specifications, it can often be
modified with additives right in the mixer
to obtain compliance with the producer’s
specifications, which are generally represented
as meeting CAN/CGSB-37.51-M90
Amazingly, over the last 30 years, neither
ASTM C24, Committee on Building Seals
and Sealants; nor ASTM D-08, Committee
on Roofing and Waterproofing, has been able
to develop a consensus standard for fluidapplied
polymer-modified rubberized
asphalt, leaving CAN/CGSB-37.51-M90 as
a default standard for minimum levels
of performance for fluid-applied polymermodified
rubberized asphalt. The CAN/
CGSB standard is cited as such in ASTM
D6622, Standard Guide for Application
of Fully Adhered Hot-Applied Reinforced
Waterproofing Systems.
CAN/CGSB-37-GP-51M was first published
in 1979 and superseded in 1990 by
CAN/CGSB 37.51-M90 by the Canadian
General Standards Board. The standard set
minimal-performance standards for rubberized
asphalt currently include:
• Flashpoint – ASTM D92
• Penetration (cone) – ASTM D1191 or
D3407 test procedure
• Flow – ASTM D1191 or D3407 test
n o v e m b e r 2 0 1 3 I n t e r f a c e • 1 1
The RCI Foundations –
Supporting The Industry
RCI Foundation – United States
Web site:
RCI Foundation – Canada
Web site:
Photo 7 – Installing rubberized asphalt wall flashings (McCormick Convention Center,
• Toughness – CGSB procedure
• Ratio of toughness to peak load –
CGSB procedure
• Adhesion rating CGSB procedure
• Water vapor permeance – ASTM E96
(Procedure E)
• Water absorption – CGSB procedure
• Pinholing – CGSB procedure
• Low-temperature flexibility – CGSB
• Crack bridging capability – CGSB
• Heat stability – CGSB procedure
• Viscosity test – CGSB procedure
Only a limited number of laboratories
have the capability to run the full battery of
CAN/CGSB- 37-GP-51M tests, generally at
a cost of $10,000 to $15,000. Unfortunately,
somewhere between very few and no jobsite
samples are actually tested for complete
specification compliance.
The initial adoption of polymer-modified
rubberized asphalt by the Canadian market
was slowly followed in the U.S. by several
large, innovative architectural firms such
as Skidmore-Owings and Merrill, I.M. Pei
and Partners, Philip Johnson,
Charles Luckman Associates,
Gwathmey-Siegel, Perkins and
Will, HOK, Michael Graves,
WDG, TAC, and similarly noted
“starchitects,” usually specifying
rubberized-asphalt systems in
inverted or protected membrane
assemblies on monumental
projects and significant architecture.
Almost consistently,
these projects had structural
concrete decks, including roof
decks, plaza decks, parking
decks, bridge decks, mud slabs,
and tunnels. A small percentage
of applications were on wood
decks, and practically no applications
were made over steel
decks until the advent of the
Type-X, moisture-resistant gypsum
and concrete underlayment
boards. Roof insulation boards
remain universally considered
as inappropriate substrates for
polymer-modified rubberized asphalt due to
the low compressive and cohesive strength
and dimensional instability of most boards.
Lightweight insulating concrete decks are
also universally considered as inappropriate
Early applications of fluid-applied rubberized
asphalt were generally unreinforced,
single-pass applications of rubberized
asphalt with a 180-mil-average thickness
specified. Flashings were usually a composite
butyl-EPDM sheet set in rubberized
asphalt, butyl side down. Today, most flashings
are 60-mil-thick, uncured neoprene
1 2 • I n t e r f a c e n o v e m b e r 2 0 1 3
Photo 8 – Typical plaza assembly: pavers, pedestals, XPS, protection course, and rubberized asphalt.
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sheet or reinforced SBS modified-bitumen sheet set with either cold
bonding adhesive or rubberized asphalt, with one supplier recommending
torched-on modified-bitumen sheet.
The early attraction to rubberized asphalt by the elite of the U.S.
architectural community was due to perceptions of ease of installation,
self-healing and self-flashing characteristics, elimination of moisture
migration below the membrane, conformability to irregular substrate
conditions, extra thickness compared to other waterproofing materials,
limited approved applicator network, wintertime subfreezing application,
no cure time, and thermoplastic characteristics, among other
features. The benefits of all these perceived features were supported
by the continual process of successful installations with few leak complaints
and near-zero systemic failures.
As previously mentioned, one of the factors in rubberized asphalt’s
earlier success was the limited network of installers. The old adage,
“The problem with roofing contractors is 80% of them give the other
20% a bad name,” is probably more true than false, and the early network
of rubberized asphalt installers was mostly drawn from the 20%
“crème de la crème” of the roof contracting community.
Workmanship—the forgotten element in many a specifier’s consideration—
is almost universally agreed upon to be the source of
most roofing and waterproofing problems with all types of moisture
n o v e m b e r 2 0 1 3 I n t e r f a c e • 1 5
Photo 9 – Completed Prudential Plaza, Chicago, 1986.
Photo 10 – Typical construction
abuse after installation.
protection systems. Polymer-modified rubberized
asphalt is no exception to that
notion, notwithstanding its higher degree
of workmanship forgiveness. The growing
awareness of the shortages of qualified craft
workers recently documented by Associated
General Contractors (AGC) comes with the
prediction that construction labor shortages
will only get worse.
Addressing the issue of workmanship
forgiveness, in the latter 1980s, most rubberized
asphalt specifications increased
fluid-applied rubberized asphalt thickness
specifications from a 180-mil single pass to
a 90-mil and 125-mil thickness, two-pass
application with a spun-bond polyester
reinforcement fabric laid in between the two
passes. This provided a level of redundancy
and a measure of additional strength,
decreasing the chances of workmanship
error by a significant margin. The improved
specification resulted in a minimum 215-
mil membrane thickness, which (with SBSprotection
course included) provided over
300 mils’ thickness of self-healing waterproofing
The most common workmanship problems
and issues that still arise with rubberized
asphalt start with proper deck and
substrate preparation, ensuring that concrete
has properly cured out; all substrates
(walls, pipes, drains, etc.) are clean and
free of contaminants; all projections are
installed; drains are operative; adjoining
walls are constructed; deck surfaces are free
of unapproved curing compounds, ridges,
and pockmarks; and other substrate irregularities
are properly addressed.
The definitive guide for concrete surface
preparation is found in ASTM D5295,
Standard Guide for Preparation of Concrete
Surfaces for Adhered (Bonded) Membrane
Waterproofing Systems. From a practical
point of view, a roofing or waterproofing
subcontractor often does not want to upset
his customer, the general contractor, with
complaints about the deck not being ready
for any of the foregoing reasons, only to
be perceived as a troublemaker, delaying
job progress. Also, there are often disputes
as to who bears the expense of proper
substrate preparation. This reluctance to
complain leaves it to the manufacturers and
QA observers to diligently supplement the
waterproofing or roofing contractor’s efforts
in this area.
The second most
common problem
regarding workmanship
(besides lack
of experience) is the
installation of flashing
materials. The
specific problem is
flashings’ not being
completely adhered
to their substrate,
creating unsupported
“bridges” and open
laps. Flashing installation
is rarely a problem
with an experienced
roofing mechanic
with a modicum
of pride in
his workmanship.
The ignorance/apathy mindset
of the “I-don’t-know” or “I-don’t-care”
worker is what manifests into problems
with the installation of flashings. All
flashing installations should be closely
inspected by QA observers and the manufacturer’s
Other less common workmanship problems
are contamination of the primed substrate
surfaces with construction dust; prolonged
overheating of material, resulting in
permanent cross-linking or vulcanization of
the product in the rubber melter; and lack
of material agitation in the rubber melter,
causing polymer segregation and resulting
in polymer-rich and polymer-lean materials’
being withdrawn from the rubber melter.
Inadequate application thickness is rarely a
1 6 • I n t e r f a c e n o v e m b e r 2 0 1 3
Photos 11A-11B – Waterproofing a high-rise
swimming pool and plaza.
problem except with polymer-modified bitumens
lacking any filler content or resulting
from overheated materials, which decreases
With just shy of 40 years of extensive
experience with this type of material, that
is about all the author has seen that can
go wrong on the workmanship side of the
equation, with the significant exception of
damage by other trades, especially after
the work is completed. While this is a forgiving
material, there is still plenty to keep
Registered Roof Observers busy.
On the design side of the equation, it
is the author’s experience that the most
common problem is lack of sufficient baseflashing
height. Architects’ tendency to value
aesthetic form over function often means
base flashings have to be invisible. This is
often possible to do by burying or cladding
the base flashings, but if it is not considered
during the design phase, it results in the
dreaded “change order,” which more often
than not means the base flashings will be
constructed too low, potentially allowing
leakage from above the flashings and then
travelling behind the flashings through the
substrate. If base flashings are not at least
8 in. above the highest expected waterline
and counterflashed, they are susceptible
to water entry and leakage. The battle over
this one detail, in the author’s experience,
seems to be neverending. Other minor
details, such as railing penetrations, safety
tie-off devices, door thresholds, and low
window-wall and curtain-wall intersections
with the deck are also sometimes inadequately
detailed and left as “field conditions”
for the contractor to improvise.
At the end of the day, fluid-applied,
polymer-modified rubberized asphalt offers
perhaps the simplest installation possible
for semiskilled workers. The thick fluidapplied
membrane is a very forgiving, redundant,
seamless, fully adhered, self-healing
waterproofing membrane. The proven longterm
performance of polymer-modified rubberized
asphalt compares very favorably
with the performance and history of oldstyle
coal-tar pitch without any of pitch’s
drawbacks—literally a space-age engineered
material installed with caveman techniques.
As the U.S. market for rubberized asphalt
continued to grow, the number of material
suppliers increased faster than the market
growth. The net effect of the increased competition
over the last ten years or so has been
the commoditization of what was formerly a
specialty, following the normal growth curve
of most successful products.
Commoditization is a double-edged
sword. Increased competition invariably
leads to greater efficiencies, promotes innovation,
and reduces costs for the building
The flip side, which is especially true of
construction materials, is it also encourages
“value engineering” and reverse engineering,
diminishing the quality of the product and
installation details and encouraging undesirable
installation compromises to which
manufacturers are susceptible in order to
stay competitive in a commodity market.
This value-engineering competition
becomes quite apparent when currently
marketed rubberized-asphalt materials are
tested for strict compliance with current
CGSB specifications. Few pass with perfect
marks, some come very close, most
come close, and a few are clearly inferior.
The deficiencies are mostly driven by the
desire to reduce costs, typically by lowering
the polymer content, adding less volume
of a needed additive, or using a few extra
pounds of filler in lieu of asphalt—all to
save a few pennies per pound. Almost all
of the rubberized asphalts sold these days
are still good or very good products, but
too many do not meet the CAN/CGSB-
37.51-M90 standards they are represented
as meeting.
In normal business/economic product
cycles, a race to the bottom usually
ends when the generic product is reverseengineered
to a failure point and then
kicked back up a notch or two or displaced
by new technology. Many “newbie”
marketers selling rubberized asphalt today
are leveraging the successful history of
the last five decades of polymer-modified,
rubberized-asphalt with products and
details that bear only a resemblance to the
products and details that created the history
of success. As anyone who has been in
the rubberized asphalt business for more
than ten years will attest, the learning curve
is a steep one.
The FuTuRe
Predicting the future of polymermodified
rubberized asphalt is as fraught
with ambiguity as any other prediction of
what the future portends.
One- or two-component fluid-applied
elastomeric membranes that are applied
cold are making some inroads in the mar-
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ketplace and offer a number of the same
features as polymer-modified rubberized
asphalt, but until they have established
a decade or two of proven success in the
North American market, they are unlikely
to replace much of the polymer-modified,
rubberized-asphalt market any time soon.
It is hard to imagine a cold-process SBS
rubberized asphalt becoming popular, as
that would require a volatile organic compound
(VOC) solvent base or a water-based
emulsion, both of which are different compounds
with significantly different properties
and characteristics than hot-applied
rubberized asphalt. Some of the differences
are environmentally objectionable, or, in the
case of emulsions, subject to the possibility
of reemulsification in certain applications.
Perhaps the most significant projected
growth area that polymer-modified rubberized
asphalt has been carving out is as the
waterproofing for vegetated (green) roofs.
De facto endorsed in the NRCA Vegetated
Roof Systems Manual as a system of choice,
with 100% adhesion to concrete decks in
a protected membrane assembly, polymermodified
rubberized asphalt offers vegetated
roofing systems the very unique feature of
decades of long-term proven success in similar
North American plaza and planter conditions
that no other generic system (other
than coal tar pitch) can honestly claim,
notwithstanding some marketing claims to
the contrary.
Roughly speaking, there are two generalized
perceptions of rubberized asphalt.
One: it is an incredibly sound, forgiving,
time-proven, trouble-free waterproofing system;
or two: it is a hot, smelly, dangerous,
gooey, archaic waterproofing system.
As the waterproofing system safeguarding
so many of North America’s monumental
structures, museums, data centers,
bridges, and other architecturally significant
structures for so many decades, the
author sides with the former perception.
For those who have been the victims of
poor workmanship or poor manufacturer
choice and those who sell other types of
competitive systems, it will always be the
latter perception.
1 8 • I n t e r f a c e n o v e m b e r 2 0 1 3
Tim Barrett, RRC, CSI, CDT, started working with rubberized
asphalt in 1975 and is the fourth-generation president of the
Barrett Company, a provider of waterproofing and roofing
systems. Barrett has served on the RCI Education Committee
since its founding 26 years ago. He chaired the original RCI
Green Roof education course development group and the
new Vegetated (Green) Roof course. Barrett has also served
on an RCI ethics panel and on the Document Competition
Committee. He is also a member of ASTM D-08, D-24, and D-60
Committees; CSI; NRCA; and Green Roofs for Healthy Cities.
Tim Barrett, RRC, CSI, CDT
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