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Coal Tar Built-Up Roofing: A Leading Solution For The 21st Century

August 15, 2009

Coal tar is still being chosen because it
is one of the most durable systems available.
Coal tar has a molecular structure
that provides a natural resistance to water,
ultraviolet rays, and chemicals – elements
commonly found on a rooftop environment.
Equally important is coal tar’s coldflow/
self-healing property, a property
offered by no other roofing product.
Although it appears solid, coal tar roofing
pitch has cold flow at normal rooftop temperature:
the warmer the temperature, the
greater the rate of flow. It is this ability to
flow that allows the membrane to continuously
adjust to changing conditions, sealing
minor fractures and abrasions that could
otherwise accelerate the membrane’s aging
process. Coal tar’s resistance to harmful
elements and its self-healing properties provide
roofs with low maintenance requirements.
It’s not uncommon to find maintained
coal tar roofs still performing after
40, 50, and even 60 years.
Longevity and resistance to hail, abuse,
and fire are just a few of the reasons coal tar
built-up roofing (BUR) systems have continued
to be a reliable choice. When compared
to some of the newer roofing systems, the
importance of the redundancy of a multi-ply
system with a flood coat and gravel surfacing
should not be overlooked. The finished
BUR system is often several times thicker
than a single-ply system.
Although the preference for built-up
roofing systems has been influenced by the
introduction of numerous single-ply systems,
the use of coal tar has also been
affected by several perceptions that have
proliferated in recent years. Coal tar – like
silica (sand), wood dust, gasoline fumes,
and other products used in the roofing
industry – has components considered to be
carcinogenic. What does this mean? If
someone improperly uses these materials,
he or she faces a potential risk. Experience
tells us, however, that just as with these
other materials, coal tar roofing products,
handled properly, can be
used safely. The industry
provides specific handling
and safety information to
workers and handlers to
help ensure proper use of
such materials. The
National Roofing
Contractors Association,
for example, has published
a number of articles
on health and safety.
Almost all roofing projects
result in some disruption
to building occupants.
On occasion, odors
are encountered by nonroofing-
related personnel
when the aroma of hotapplied
roofing materials such as asphalt or
coal tar comes through open windows or air
vents during roof construction. This has
caused concern in some instances. Certain
steps can be taken to reduce and control
fuming, such as maintaining proper material
temperatures and positioning kettles or
tankers well away from building air intakes.
Roofing work can also be performed when a
building is unoccupied.
Another misconception relates to limited
geographic applications for coal tar roofing
systems. Coal tar roofing products and
systems are available in all North American
markets. Although there are some roofing
contractors who choose not to install coal
tar systems, there is a nationwide network
of contractors who promote and install coal
tar systems on a regular basis.
Until recently, coal tar and asphalt
built-up roofs (collectively referred to as
BUR systems) represented the norm in the
low-slope commercial roofing industry for
more than a century. Technologies, including
single-ply and polymer-modified bitumen
(mod bit) membrane systems, have
attracted a significant portion of this market.
Most of these systems present a type of
innovative change, though often, an innovation
in one area compromises another. For
example, systems that demonstrate an easier
and faster installation often cannot
match the long-term performance of systems
that may take longer to install. On the
other hand, a newer system, designed for
long-term performance, typically carries a
higher cost. Although customers would like
the best of both worlds, building owners,
specifiers, and roofing contractors will continue
to be challenged to determine the true
Workers applying a roof restoration coating. value of a roof and compare that to cus-
8 • IN T E R FA C E S E P T E M B E R 2009
tomer objectives and budget.
Economical, durable, and
long-lasting coal tar roof
systems appear to once
again be gaining the support
of building owners and roofing
Coal tar BUR is also considered
one of the best systems
to install in applications
with unique and specific
requirements. Coal tar
is an ideal product to use
where a roof will be subjected
to common or continuous
stand ing water. In some
cities, there are regulations
identifying how fast water
can drain off a roof in order
to avoid overtaxing sewer systems. Rooftop
runoff management effectively increases the
time of concentration of runoff derived from
roofs, delaying runoff peaks, lowering
runoff discharge rates, and sometimes even
generating sewer cost savings. A coal tar
system is also ideal for vegetated “green”
roofs, where the system is going to be continually
Things have changed significantly since
the time when coal tar and asphalt BUR
dominated the low-slope roofing market.
The low-slope industry has become much
more complex. A variety of different systems
has flooded the marketplace, and building
owners are now confronted with the decision
of choosing between EDPM, PVC, TPO,
Hypalon, mod bit, and BUR — just to name
a few. Each has its own characteristics,
physical properties, recommended uses,
and performance history. While some of
these roofing systems have performed well
when installed properly, others have not
lived up to customer expectations, often in
unexpected ways. Asphalt and coal tar systems
still play a vital role in the low-slope
roofing industry. Asphalt plays a key role in
BUR and mod bit systems. Coal tar, often
thought to be a product of the past, is gaining
popularity, not only in its traditional
form as a built-up roof, but also in several
other forms. Polymer-modified coal tar
membranes and polymer-modified, mopping-
grade coal tar pitches are gaining
widespread market attention.
The top surface of a roofing membrane
is the weathering layer. A key attribute of
coal tar is its ability to be maintained and
restored so that a well-cared-for roof can
last almost indefinitely. However, it is
important not to delay maintenance and/or
restoration until the roofing system is
beyond the point where it can be economically
restored. It can be far more expensive
to replace a roof than to properly maintain
it, especially if the system is allowed to deteriorate
to the point where the deck needs to
be repaired or replaced, as well.
The objective of the restoration process
is to keep the weathering layer performing
its duty.
A facility that has implemented a roof
management program will have an inventory
that places each roof area into one of the
following categories:
These roofs appear to be in sound condition.
They should be scheduled for periodic
inspections, usually twice a year, in
spring and fall. Regular inspections are key
to keeping good roofs in sound condition.
These roofs will have reasonably minor
problems, such as bare spots on graveled
roofs, open laps in the flashing membrane, or
deteriorated sealant at the counterflashing.
These roofs are in need of more than
just minor repairs and can be returned to
good condition with some reasonable attention.
These may include a granulated membrane
roof with surface cracking and loss of
granules that is in need of a new surface
coat and granules; equipment curb and wall
flashings with deteriorated surfacing in
Roofing contractors &
specifiers choose Durapax
coal tar roofing systems.
Coal Tar:
First Choice for Flat Roofs
First Choice in Coal Tar
• Coal tar roofing provides low cost and
long life (25+ years)
• Many coal tar roofs last more than
50 years
• Coal tar’s cold flow properties provide
• Superior technical & customer support
• Delivery you can depend on
• Comprehensive warranties
• UL & FM approved systems
Specify your next flat roof with a
Durapax coal tar roofing system.
S E P T E M B E R 2009 I N T E R FA C E • 9
A worker applying a hot flood coat onto a BUR system.
need of resurfacing; and graveled roofs with
bare spots that are in need of new flood
These roofs have extensive problems,
and it would not be considered a good
investment to spend capital trying to maintain
or restore them.
Before restoration can begin, one must
first determine the type of bitumen used in
constructing the roof system. One can
determine the difference between coal tar
and asphalt by the odor, a solubility test, or
laboratory identification.
Before applying a restoration coating or
flood coat and aggregate, the roof system
must be properly prepared. The type of
restoration coating to be used will be based
primarily on the preferred method of application.
A coal tar pitch, built-up, gravelsurfaced
roof can be restored by using
either a cold or a hot method. The cold
process method typically uses a solventborne
coal tar such as a resaturant (for
organic felts) or a coal tar polymer coating.
Due to the solvent-borne coal tar’s unique
penetrating qualities, this
material will be absorbed
well into the structure of
any coal tar BUR membrane,
adding flexibility
and new life to an aging
system. In addition, there
is no need for a roofing kettle,
which is preferable in
some situations due to the
building owner’s preference
or the logistics of the
project. A new flood coat of
hot coal tar roofing pitch
can also be used. A flood
coat doesn’t have the
extended cure time of a
solvent-borne product and
it is usually more economical
than a coal tar resaturant
or other solvent-borne coating, es –
pecially for larger roof restorations.
Prior to the application of a restoration
coating or new flood coat and aggregate surfacing,
all necessary repairs should be
made, including replacing any wet insulation
and replacing or making appropriate
repairs to deteriorated parts of the roofing
system, typically matching the original system
to the greatest degree possible. If the
restoration (coal tar resaturant, coal tar
polymer coating, or flood coat and aggregate)
is going to add weight to the system,
then consideration should be given to
whether the existing structural components
can handle the additional load. After the
preliminary preparation has been completed,
the surface receiving the restoration
coating must be dry and free of any dirt or
loose debris. The rates and procedures of
application vary between coatings and manufacturers.
Typically, the loose aggregate is
removed from the surface, the coating or
new flood coat and aggregate is applied, and
new aggregate is embedded.
Coal tar BUR systems offer building
owners a variety of benefits. On a life cycle
cost basis, there are few commercial roofing
systems that have outperformed coal tar.
Years of service, coupled with maintenance
cost and all other factors commonly
included in the life cycle equation, determine
a product’s life cycle cost. Pound for
pound, coal tar has traditionally been more
expensive than its asphalt counterpart. On
the other hand, due to the slope requirements,
the installed cost of a coal tar system
can be less than an asphalt or singleply
roofing system. Because of coal tar’s
inherent resistance to water, slope is not a
prerequisite. Coal tar suppliers offer warranty
coverage, which does not exclude
ponded water areas.
Coal tar is alive and well, has an unparalleled
performance history, and continues
to offer benefits that have often been overlooked
in recent years. Coal tar is receiving
well-deserved consideration by the qualityand
cost-conscious consumer.
The layering technique for applying the reinforcing plies,
topped with aggregate embedded in a flood coat of coal tar
roofing pitch, maximizes the life span of this roofing system.
Kevin Ochis is the president of Durapax Coal Tar Commercial
Roofing Systems. In his current role, Kevin focuses on growing
Durapax and providing building owners and specifiers
with coal tar built-up roofing products and systems. Kevin
has worked in various positions at a major manufacturer, filling
financial, marketing, and operations roles before being
promoted to lead the roofing division. Kevin has a BS from
Penn State University and an MBA from Duke University. He
can be reached at
Kevin Ochis
10 • I N T E R FA C E S E P T E M B E R 2009