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Electronic Leak Detection: The Future of Membrane Integrity Testing

May 15, 2013

6 • I n t e r f a c e A u g u s t 2 0 1 3
Electronic leak detection (ELD),
the next generation in nondestructive
membrane testing,
is rapidly becoming the
first choice for manufacturers,
specifiers, consultants, and
contractors around the world. It is providing
faster, safer, more accurate, and less
expensive leak locating and integrity testing
on waterproofing and roofing membranes,
pinpointing leaks directly so they can be
immediately repaired and retested.
However, as often happens with new
techniques, many people find themselves
unfamiliar with the functional details of the
technology, the principles employed, and
the procedures followed when performing
the inspection. In fact, familiarity with these
issues can help ensure the testing will be
conducted in the optimal
manner and yield accurate
In this article we will
provide an overview of the
benefits of ELD over traditional
flood testing, describe
the two most commonly employed types of
ELD, and identify important considerations
when specifying and purchasing these testing
services. Note: While ELD goes by several
trade names (e.g., electronic field vector
mapping [EFVM®], Integriscan™, etc.), for
the purposes of this
discussion, all electrically
based integrity
testing will be referred
to as ELD, either highor
Electronic Lea k
Detection vs .
Flood Testin g
Traditional flood
testing can be timeconsuming
and expensive,
especially when
retesting is required.
The load-carrying capacity
of the building
and the weight of the
required water must be
clearly understood in
order to avoid potentially
catastrophic damage.
If leaks are present,
flood testing can
cause significant water
damage within the
building. Flood testing
doesn’t pinpoint membrane
breaches; locating
leaks still requires
visual inspection and
one or more additional tests.
ELD is quick and safe, as high-voltage
testing is performed on dry membranes and
low-voltage inspections require only wetting
Figure 1 – Probe and trace wire low-voltage vector mapping pinpoints breaches by
interpreting the direction of current vectors across a moistened membrane.
Figure 2 –
performing probe
and trace wire
method of lowvoltage
mapping on a wet
the membrane, not flooding. Unlike flood
testing, inspections pinpoint the actual
breaches for immediate repair and retesting.
Even pinholes too small to be seen can be
quickly located. In addition, breaches can
even be isolated on many roofs with overburden.
The test techniques are also easy
to apply to vertical surfaces, and significant
time and expense can be saved by not having
to dam sloped areas.
Princip les and App lications
In order for ELD to be performed, two
conditions must be met: First, the membrane
must be nonconductive (i.e., have
a high dieletric strength); and second, a
conductive grounding medium (typically
a structural concrete or metal deck or
metal mesh) must be present beneath the
membrane. Fortunately, most roofing and
waterproofing membranes are nonconductive
and are excellent candidates for ELD.
One notable exception is black M-class
ethylene propylene diene monomer (EPDM)
rubber membrane, which contains carbon
black, an electrically conductive substance.
Integrity testing on EPDM membranes is
typically conducted with infrared cameras
and/or nuclear moisture gauges, as ELD
will not work on this material.
An ELD device works by creating an
electrical field on the membrane surface
and a second electrical field in a ground in
the system. Although the voltages vary, the
ELD equipment generates only a very small
amount of current, so electrical hazards are
When the electric field on the membrane
surface encounters a breach, electricity
travels from the roofing/waterproofing
membrane surface through the breach to
the grounding medium below. This completes
the circuit, triggering the testing
device to alert the technician that a breach
has been detected. The technician then uses
the test equipment to pinpoint the location
of the breach.
There are two types of ELD surveys—
low-voltage and high-voltage—sometimes
referred to as “low-voltage electrical conductance
testing” and “high-voltage spark
testing.” Both types use a mobile batterypowered
electrical generator to create the
necessary electrical charge. Each type has
its particular advantages and limitations.
Selecting the most appropriate technique
for each particular application will minimize
costs and enable the technician to obtain the
most thorough and accurate testing results.
Although manufacturers have developed
two distinctly different approaches to
low-voltage ELD, both are performed on a
wet surface and find leaks when the current
connects to ground through the moisture.
Probe and Trace Wire Low –
Volta ge Vector Mappin g
For low-voltage devices that use handheld
probes to detect current flow through
breaches, the test area is prepared by laying
a loop of exposed metal wire (referred to as
a trace wire) on the membrane around the
perimeter (Figure 1). To prevent false-positive
readings, grounded penetrations within the
test area are isolated using wire loops that
are connected to the perimeter trace wire.
The completed trace wire is then connected
to one terminal of a pulse generator. The
other terminal of the generator is attached
to a ground connected to the structural
deck of the system (usually a drain, railing,
etc.) or to an alternative-grounding medium
installed in the system.
A u g u s t 2 0 1 3 I n t e r f a c e • 7
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8 • I n t e r f a c e A u g u s t 2 0 1 3
A pulsating electrical current (typically
38-40 volts DC) is introduced into the trace
wire. An electrical field is maintained above
the membrane by spraying water on the
membrane surface to keep it completely
moistened (not flooded). The size of the test
area is governed by surface conditions of the
membrane, the ability to maintain surface
moisture, and the equipment used.
Using two metal sensor poles connected
to a detector unit (potentiometer), the technician
methodically surveys the test area
while monitoring the detector (Figure 2).
When no membrane breaches are present,
the electric current in the test bed is static,
with no significant current vectors. When
there are breaches, the potentiometer senses
electrical flow across the field as current
travels from the trace wire to the breach
where it is grounded, and the circuit is completed.
The technician follows the current
direction until the breach is pinpointed.
When multiple breaches are present, each
individual fault must be either repaired or
isolated from the test bed with a temporary
wire loop connected to the perimeter trace
wire. This effectively “screens” or removes
the breach from the inspected area. The
technician then resumes the testing until all
breaches have been identified.
Because a significant advantage of ELD
is that detected breaches can be quickly
repaired and retested, the ideal situation is
for the membrane installation contractor to
be on site during the testing. This way, any
faults can be repaired and retested; and at
the conclusion of the testing,
the membrane can be certified
breach-free. If the membrane
will receive overburden, the
trace wire is usually left in
place and connection boxes
are provided so that lowvoltage
leak detection can be
performed after the installation
of the overburden.
Scannin g Dec k Low –
Volta ge Testin g
A second type of lowvoltage
test device employs
a roughly 1.5- x 2-ft. mobile
“scanning deck” that is
pushed over a continuously
moistened membrane surface
(Figure 3). Small metal chains
hanging from the outer edges
of the deck take the place of
the trace wire. A similar array
of chains hangs from the inner part of the
deck, and both sets of chains are connected
to the device’s power generator. When
the deck passes over a membrane breach,
there is a change in the electrical potential
between the two chain arrays, and the testing
technician is alerted that current has
connected to ground directly beneath the
Hi gh-Volta ge Spar k Testin g
High-voltage ELD works on the principle
of arcing: the passage of electrical current
through a normally nonconductive medium
such as air. Typically, high-voltage ELD
equipment has adjustable current outputs
from 1,000-30,000 volts DC. This allows for
testing membranes from a thickness of a
few mils up to 1/2 to 5/8 in. In addition to
the high-voltage arcing, if moisture is present
in the system, it will act as a conductive
path for completing the circuit.
This test is conducted on a dry membrane
surface, so a water source is not
required. Although sometimes referred to
as “high-voltage vector mapping,” in highvoltage
testing, the technician locates
breaches directly rather than through interpretation
of current vectors. Thus, there is
no need to lay a trace wire or isolate penetrations
and located breaches from the rest
of the test area.
Technicians employ a broom-like metal
brush, typically 2 to 3 ft. wide, connected
to one terminal of the generator. The other
terminal of the generator is connected to the
structural deck or other grounding medium
(Figure 4). The technician walks in straight
lines across the membrane surface, pushing
or pulling the electrically charged brush
(Figure 5). When the brush passes over a
breach, current travels through the breach
to the ground. The completed electrical circuit
triggers an audible alarm to alert the
technician, who then uses a corner of the
brush to pinpoint the exact breach location.
The current is capable of arcing through air
(up to 3/4 in.), so water does not have to be
present in the system; but if the schedule
permits, it can be helpful to have the membrane
experience several rain events.
Figure 3 – Scanning deck method of low-voltage testing
uses metal chains hanging from the deck instead of a
trace wire and probes.
Figure 4 – High-voltage ELD locates breaches directly when the current arcs through a
breach to ground.
In systems where there are nonconductive
materials between the membrane
and the structural deck (e.g.,
insulation or vapor retarders), it may
be necessary to install an alternative
grounding medium as close to
the membrane surface as possible.
Stainless steel and aluminum meshes
are commonly employed to act as alternative
grounds, while conductive felts
are often employed in modified-bitumen
and built-up systems.
Low Volta ge or Hi gh?
Because there is no need for trace
wire and it is not necessary to wet the
membrane, high-voltage testing may
take less time than low-voltage, particularly
if there are many grounded
penetrations or numerous breaches.
It is also excellent for testing vertical
surfaces such as curbs, parapets,
and foundation walls, because there
is no need to maintain a moist surface
(Figure 6). However, the test surface
must be completely dry, and ponded
water or even dew will create unstable
test conditions. Low-voltage testing
typically requires a second person to
spray water and maintain moisture on
the membrane, while a single technician
can conduct high-voltage testing.
High-voltage testing requires that the
electrically charged brush be in contact
with the membrane and is not suitable for
testing systems with overburden (vegetation,
pavers, ballast, etc.). If the overburden
can be sufficiently wetted and a trace
wire is installed at the perimeter, lowvoltage
testing can usually deliver sound
test results with these overburden materials
in place. It is common practice to utilize
ELD as an integrity test of the waterproofing
membrane prior to the installation of any
overburden, in which case either method
may be used.
Specif yin g Electronic Lea k
Because these testing methodologies
are relatively new and specifiers and consultants
are often unfamiliar with the technology,
ELD specifications are sometimes
incomplete or inaccurate.
The specifications may fail to adequately
define the equipment to be employed, procedures
to be followed, qualifications of the
testing agency, or requirements for the final
report. In some cases, ELD may be specified
on systems that, as designed, cannot
be inspected with an electric current technique.
When in doubt, specifiers can work
with experienced ELD providers in order to
ensure accurate and complete specifications
are employed.
Purc hasin g Third -Part y ELD
Several considerations are important
when evaluating and purchasing these
third-party services:
• Construction schedules are often
tight and demanding. Be certain
that the testing firm can adequately
respond to scheduling needs.
• In order to utilize the best test
methodology and generate accurate
results, it is critical that the
ELD technician be provided with
complete and accurate information
about the assembly being inspected.
• As with all nondestructive testing
techniques, training and experience
are essential for high-quality, accurate
test results. Be sure that the
technician has adequate experience
with the testing techniques employed
and the assembly being inspected.
Bri ght Future
Electronic leak detection is a major
step forward for the waterproofing and
roofing industries. It is already saving
significant time and money and improving
the ability of all parties to deliver higherquality,
more trouble-free products and
services. Look for ELD to play a greater
and greater role in quality control and leak
investigations for both roofing and waterproofing
A u g u s t 2 0 1 3 I n t e r f a c e • 9
Peter Brooks is president of Vector Mapping/IR Analyzers. He
has been performing nondestructive testing for over 31 years
and is currently director of RCI Region I. He may be contacted
Peter Brooks
Figure 6 – High-voltage
testing is excellent
for vertical surfaces
and congested areas.
Figure 5 – High-voltage ELD
is conducted by sweeping
a dry membrane with an
electrified brush.