Flat roof leak detection - the wet method
Flat roofs can develop leaks for a variety of reasons and at any point in their lifespan. Workers can accidentally (and unknowingly) pierce a roof’s waterproof membrane even before construction is completed.
Extreme weather, debris, poor design and poor construction can all conspire to create leaks. These leaks are often too small to spot with the naked eye yet, if left, can cause substantial damage to a building’s structure in no time at all. Detecting and repairing leaks in flat roofs at the earliest opportunity simply makes sense; especially if there is a simple and time efficient way of quickly locating leaks.
Nowadays the vast majority of flat roofs are constructed from electrically conductive materials such as steel or concrete and many have a foil-faced insulation layer directly below the surface membrane. Buckleys’ leak detectors use the conductive properties of these materials to locate faults by passing current through defects to earth.
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Testing Wet Roof surfaces
The winter months (and many of the summer months, depending on where you are in the world), can be very wet – making the dry method of testing impossible.
The Wet Roof Pro’ has been designed to locate leaks on flat roofing systems which incorporate dielectric membrane overlays such as single-ply, asphalt, bitumen and liquid applied roofs. It uses the conductive properties of water (from either rainfall or a hose) to pinpoint leaks.
The kit comprises two main elements; a generator unit and a detector unit. The generator unit creates an electrical field across the roof surface via a ‘boundary wire’ which is positioned around the perimeter of the test area and connected to the negative terminal on the generator unit. The positive terminal is connected to a suitable earth on the building’s structure.
Leaks in the roof membrane allow water to penetrate to the building’s structure; creating an electrical circuit. The detector unit is connected to two hand-held test probes which are held in contact with the roof surface. By measuring the voltage differential between the test probes, the detector unit is able to direct the operator to the location of the leak.
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Principle of operation
The generator of the Wet Roof Leak Detector delivers a stabilised low frequency pulse. The negative output of the generator is applied to the trace wire which borders the test area, whilst the positive output is connected to a suitable building substrate. If moisture has penetrated the membrane or coating of the roof within the test area, a current will flow from this source point, via the moisture on the roof towards the trace wire.
The detector is used to identify the direction of electrical current and detect the point of origin (ie where moisture is penetrating the roof covering). The generator is powered by rechargeable batteries which are included in the kit, along with a charger. Both units feature automatic shut-down when left unused for a prolonged period of time.
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Some important specifications:
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Method of testing
The test procedure is performed within a test area, created with stainless steel wire, which must be in good contact with the wet surface. If necessary, weights or adhesive tape should be used to hold the wire in position and the ends of the wire must be clipped together to form a closed circuit (ring).
Any areas which protrude from the roof must be screened off by using an additional loop of wire, which in turn must be connected to the main border. Test electrodes are supplied in three parts which can be put together easily on site to form two probes (poles). These are connected to the small detector unit with the red and black leads supplied.
A suitable mechanically-fixed earthing point should be located on the building. Using the crocodile clip, the 10-metre lead (with red plug) should be securely attached to the earth point whilst the other end is connected into the positive (red) socket of the generator unit. The black plug on the other connecting lead should be fitted into the negative (black) socket on the generator unit with the crocodile clip attached to the trace wire. The clip must be positioned to clamp together the free end of the trace wire to the section of wire emerging from the reel to complete the loop around the test area. The generator unit should now be switched on.
When the detector unit is switched on the unit will self-calibrate ― it is important that the probes are not in contact with the test area at this point. The red probe should be held in the right hand and the black in the left, making sure that the leads do not cross over. Inside the test area, the probes should be positioned a distance apart either side of the body in contact with the wet roof. When the generator pulses the bar graph on the detector unit will show the direction of the fault. Starting at the edge of the screened area, re-positioning the probes and watching the detector will locate the direction of the fault (right or left). You will get the strongest signal when the two poles are in line with the fault. The search is continued in the direction of the pulse until the reading swings the opposite way. At this point, if the operator turns 90 degrees and repeats the procedure a crossover point can be reached to locate the source of the leak.
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Criteria for successful testing
There are a number of criteria that need to be met for successful detection of membrane faults:
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In ideal conditions, the Wet Roof Pro’ can test up to 4000m2 per day.
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