Excess moisture trapped in roofing or waterproofing assemblies can have a negative impact on performance, and also lead to premature failures. Employing an electrical impedance scanner is a an efficient way to conduct moisture surveys of roofing and waterproofing systems.
A new ASTM International standard—D7954/D7954M, Practice for Moisture Surveying of Roofing and Waterproofing Systems Using Non-Destructive Electrical Impedance Scanners—covers the use of electrical impedance scanners to monitor the moisture level of a roofing system over various stages of its lifespan.
“As the practice of using electrical impedance scanners to locate moisture and evaluate the comparative moisture levels within roofing and waterproofing systems is widely used, it is important to have an ASTM standard in place that would qualify the types of moisture scanner suitable for this purpose,” explained Sean Fallon, a member of Subcommittee D08.20 on Roofing Membrane Systems.
In the described procedure, an electrical impedance scanner is moved across a roof surface. Low-frequency signals are transmitted non-destructively through the surface, measuring the electrical alternating current impedance. The strength of the signal varies in proportion to the moisture level under the footprint of the scanner, with greater amounts of moisture resulting in higher comparative moisture readings.
ASTM D7954/D7954M can be used during a roofing/waterproofing assembly’s installation to determine whether there was moisture intrusion into the system or materials. However, it can also be employed at regular intervals as part of a preventive maintenance program or before repair work to determine the extent of amelioration necessary.