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COATINGSPRO SURFACE PREP 2018 41 Moisture Monitoring dedicated to testing large roof areas whereas other methods may take just hours. e roof surface must be completely dry for the high voltage method and must be completely wet for the low voltage method. In both cases, the material under the membrane (i.e., the decking) must be a good conductor of electricity to allow a current to pass through the material using available moisture as the conductor. In this case, timber decks are not suitable. e technique does not work on all roof types. e membrane under test must not be a conductor of electricity. For example, black EPDM membranes with a high carbon black content are known to conduct electricity, and the technique will not work on these roofs. Specialist knowledge and experience are again necessary for these test methods, and, in the case of the high voltage method, getting the voltage right to suit the membrane type and thickness is vital to ensure holes are not missed. Lastly, these methods do not find where the moisture has spread within the roof, nor will they detect moisture that may ingress through joints or flaps where membranes join together. New Methods Some interesting new products have come to the market to provide ongoing monitoring of roof moisture conditions. e more reasonably priced products require manual inspection using a handheld device, which communicates with the in-situ probes to give a reading of "normal " or "critical." Some systems can be wired in and, working on the basis that a roof will always contain some level of moisture, when the level reaches a critical point, an alarm is raised. Obviously, these are the more expensive variety. Electrical impedance/capacitance testing is surprisingly easy to use and fast, covering large roofs of up to 100,000 square feet (9,290.3 m²) in a normal working day with a single unit. is tests to ASTM D7954: Standard Practice for Moisture Surveying of Roofing and Waterproofing Systems Using Non-Destructive Electrical Impedance Scanners, which refers to testing techniques that use two types of non-destructive electrical impedance scanners on flat roofing: continuous and point-of-contact. ese methods allow for surveying of moisture conditions in roofing and waterproofing systems to a nominal depth of 6 inches (15.2 cm). It can be used during normal daylight hours without the need to clear the occupants of the building or even to remove ballast, so long as the ballast is of a suitable thickness and is not overly wet. Continuous scanning is carried out with a "mobile- wheeled scanner" that is pushed across the surface of the roofing or waterproofing system in a row-by-row or grid format methodology. e scanner will obtain continuous comparative readings, allowing for the localization of excess trapped moisture within large flat roof surface areas. e The makeup of the roof is made of can often affect which moisture detection system should be used. Continuous readings from a "mobile-wheeled scanner," for example, can be useful on large flat surfaces.

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