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Electric Field Vector Mapping (EFVM)

May 15, 2002

Operation Principle
The EFVM technique uses water as an electrically
conductive medium; therefore, it is
essential that the surface to be tested is wet. If it
is not raining at the time of the survey, then
water needs to be sprayed over the area. Once
the area is suitable for the test, the survey technician
installs an un-insulated wire loop around
the perimeter of the area and connects the electrical
pulse generator to the wire. The electrical
pulse generator delivers a 40-volt potential for
one second every three seconds. The pulsating
potential on the wet roof surface forms an “electrical
plate.” The grounded structural deck is the
other “electrical plate,” while the membrane
separating the two plates acts as the insulator. If
moisture enters a breach in the membrane, an
electrical contact is established between the two
plates (i.e., an electrical ground).
Using a potentiometer connected to two
probes, the survey technician steps into the
Figure 1: EFVM operation principles.
June 2002 Interface • 3
By Chris Eichhorn, RRO
INTRODUCTION
Electric Field Vector Mapping (EFVM) is a new and powerful tool for improving quality control on waterproofing systems.
Although this method is unfamiliar to most North Americans, it has already achieved a long record of success in
Europe. Unlike most other leak detection methods, it can locate the point of entry quickly and accurately. Another unique
aspect of this technique is that a pinhole (too small to find visually) is as easy to locate as a large tear or failed seam.
Alternative approaches, like infrared surveys, can determine where water has accumulated in the roof insulation but may not
be as useful in actually finding the waterproofing defect. The traditional flood test also has its practical problems. If the
membrane is not watertight, the roofing substrate could become saturated and permanently damaged. After the water is
drained off, the punctures still have to be located. Therefore, the EFVM test has become Europe’s most widely-used, nondestructive
test method for detecting leaks in membrane roofs.
(EFVM)
electric field and places the probes on the surface. If there is a
breach in the membrane, the dial on the potentiometer will
move either to the left or to the right. The survey technician can
then follow the direction of the electric field to the membrane
breach. Because of the high electrical resistance through the
roof, the magnitude of the electrical current is relatively small.
However, the magnitude of the
current is not important, but the
direction of the current flow is
what leads the survey technician to
the breach.
Benefits of EFVM
The benefits for EFVM can be
summarized as follows:
• Ability to locate defects
precisely and non-destructively.
• Ability to re-test repairs
immediately.
• Can be used after cover
systems are installed,
especially with “green roof”
landscapes.
• Eliminates the hazard of
overloading structural decks
during testing, since ponding
water is not part of the
testing procedure.
• Can be used on sloped roof
surfaces where flood testing
is impossible.
4 • Interface June 2002
Figure 2: Leak investigation on a green roof in Frankfurt, Germany.
Applications
EFVM has been used successfully with a wide range of waterproofing
materials. AB Flachdach, a leak detection company in
Germany, has electronically surveyed in excess of 35 million
square feet of roof membrane within the past five years. The
suitability of EFVM depends on the electrical resistance of the
waterproofing materials. As an example, EPDM membranes,
which contain carbon black, are generally not suitable due to
their normally all-too-high electric conductivity. Aluminized
protective coatings, commonly used in North America in conjunction
with modified bituminous membranes, may also defeat
the technique. However, International Leak Detection Ltd., a
North American affiliate of AB Flachdach, can conduct benchscale
tests in order to establish that EFVM is suitable for a particular
waterproofing material. EFVM can be used on all types of
structural roof decks, including metal, concrete, and wood. (A
special “grounding grid” must be introduced on top of the wood
deck in this case.)
The EFVM method has proven highly advantageous in situations
where the waterproofing is concealed or buried. These
include IRMA (Inverted Roof Membrane Assembly) configurations,
plaza installations, ballasted roofs, and “green roofs.”
Green roofs are veneer landscapes installed on top of conventional
roofs. They may be anywhere from 2.5 inches to 3
feet deep.
Without an effective method of locating defects, leak location
and repair can become very expensive on these systems.
Currently, EVFM is being used by Roofscapes Inc., a green roof
provider, on numerous green roof projects in North America,
including South River Colony office building in Maryland, Point
Defiance Zoo in Washington State, and a large chiropractic center
in Pennsylvania.
EVFM was used as a quality control measure at the Chek Lap
Kok Airport in Hong Kong. A total of 165,000 square feet was
electronically surveyed, and over 100 breaches were located in
the membrane. The contractor was still on site at the time of the
testing and repaired the breaches on a daily basis. The repaired
areas were tested upon completion by the survey technicians to
ensure the membrane was 100% watertight. A new addition,
presently at the developmental stage, will include the EFVM test
as part of the specifications.
A recent project in Frankfurt, Germany, further illustrates the
value of EFVM as an asset management technique. This project
involved an 110,000 square foot roof that was installed in 2000.
The technicians found 17 defects in the membrane. Some of
these flaws were located in defective seams (workmanship) while
others were found to be tiny punctures. There was no visible
water damage in the interior of the building. The building owners
did not know that there were any problems and probably
would not have found the flaws until the insulation had
become saturated.
Geo-membrane liners and/or containment liners are also beneficiaries
of the EFVM test. These membranes can be tested for
any defects prior to commissioning their use and, depending on
the depth of the containment basins, also during their use.
Conclusion
EVFM testing is a practical alternative to flood testing low
slope roofs, waterproofing membranes, and geo-membrane liners
and is an invaluable tool for our industry. Application of the
non-destructive test method includes checking the integrity of
newly installed roof membrane systems as part of a quality control
procedure and assessing the waterproofing integrity of aged
roofs. The greater and more widespread use of the EFVM test as
an objective method for positively identifying breaches in membranes
is likely to contribute to confidence in the perf o rmance of
w a t e r p roofing membranes for the future. n
REFERENCES
• Roberts, Keith, “The Electrical Earth Leakage Technique
for Locating Holes in membranes,” P roceedings of the Fourt h
I n t e rnational Symposium on Roofing Te c h n o l o g y, September 1997.
• Burger, Klause, “Stararchitekt fordert Uberprufing der
Dachabdichtung,” Know How, Germany, December 1999.
Figure 4: Locating leaks in a geo-membrane liner with the
EFVM technique.
Figure 3: Leak detection at Chek Lap Kok airport, Hong Kong. Applying
continuous flow of water on the sloped PVC membrane to facilitate the test.
June 2002 Interface • 5
The U.S. Department of Labor
has projected a rapid growth in
demand for environmental engineers
and architects over the next ten
years. The field for architects could
grow from 102,000 in 2000 to
121,000 in 2010. The following table shows
projected growth in related professions from 2000 to 2010.
2000 2010 % change
Architects 102 121 18.5%
Environmental eng. 52 66 26.0%
Construction trades 6,466 7,328 13.3%
Civil engineers 232 256 10.2%
June 2002 Interface • 7
• Thornton, Steve,
“Electronic Leak
Detection,” Interface,
February 2001.
• Granne, Fredrik, “Air
and Water Tightness in
Building Envelopes—
Evaluation of Methods
for Quality Assurance,”
Doctoral Thesis,
November 2001
• Miller, Charlie, and
Eichhorn, Chris, “A
New Leak Detection
Technique,” New York
Real Estate Journal,
January 2002
ABOUT THE AUTHOR
Chris Eichhorn, RRO, is president
and founder of International Leak
Detection, Ltd., a company specializing
in membrane leak detection services
across North America. Mr.
Eichhorn has been involved in the
roofing industry since 1977. Chris has
served on the Board of Directors and
is past Chairman of the Membership
Committee of the Ontario Industrial
Roofing Contractor Association and
currently serves on the Board of
Directors of RCI, Ontario Chapter, as
its Technical Director.
CHRIS EICHHORN,
RRO
Another effect of the September ter rorist attacks has been
the refusal, by most major insurance firms, to provide insurance
coverage for future losses due to terrorism. As a result,
there is a movement to establish a federal safety net to encourage
the property and casualty insurance industry to continue
offering such coverage.
The proposals currently before both the Senate and the
House of Representatives would provide a federal reinsurance
partnership and co-payment of damage claims over a set
amount for a period of short duration, such as 3-5 years.
Disagreements remain in both parties, especially over whether
to protect corporations and insurance companies from lawsuits
over inadequate safeguards against terrorism.
—SMACNA News
N N
Figure 5: Leak detection procedure on an
inverted BUR roof system. Locating
b reach through the ballast and insulation.
DOL FORECASTS JOB GROWTH
PostScript Picture
(STEEL… TITLE TREATMENT.eps)
President Bush placed tariffs of 8 to 30% on steel imported
from Asia, Europe, and South America on March 5. The
tariffs exclude NAFTA nations and 80 other “developing”
countries and will be in effect for three years.
The European Union has announced it will fight the tariffs
in the World Trade Organization, which has international
authority in trade disputes. The tariffs are meant to
protect the bruised American steel industry.
(In Thousands)