Electrical Capacitance Testing (ECT)

RAM CONSULTANCY LTD
ELECTRICAL CAPACITANCE TESTING (ECT)

Electrical Capacitance Testing (ECT) | Moisture Mapping Surveys

The most common non-destructive testing technique used on the flat roofs is electrical conductance testing (earth leak testing). This testing works on the principal that the structural roof deck is an electrical conductor and the waterproofing membrane is an electrical insulator.

On some roofs the structural roof deck is timber and technically this earth leakage testing cannot be used. An alternative non-destructive electrical testing technique, electrical capacitance testing can be used to map out areas of entrapped water below a waterproofing membrane. RAM Consultancy Limited have a range of non-destructive techniques to determine if moisture is trapped within the roof construction. Two of these techniques are capacitance moisture meters; a hand-held LeakSeeker and wheel-mounted DecScanner. The instruments transmit electrical pulses into the roof construction and measure the ability of the substrate to hold an electric charge.

Relative damp areas hold less charge and an audible and visible signal indicates that water may be present. Moving the instrument across the roof surface can identify the area of entrapped water. The affected areas can be marked on the roof and on a roof plan included in the report.

Electrical Capacitance Testing (ECT) | Moisture Mapping Surveys

A test technician undertaking an electrical capacitance survey (ECT) on a roof surface to identify areas of entrapped water prior to commencement of the DeWatering

The roof surface must be an electrical insulator, the capacitance survey will not work on metal-faced felts or some other electrically conductive roof finished such as some silver reflective paints. Before surveying the roof surface must be dry.

The instrument is calibrated and the survey undertaken by systematically covering the roof, ensuring that all the roof area is surveyed. Core samples may be taken at a 'wet' and 'dry' area to confirm the readings of the instrument and that there is no component within the roof construction that could be giving spurious results.

Alternatively the test equipment is calibrated in an area where there are no reported leaks below and the insulation/deck is assumed to be dry.

The survey is completed with any 'wet' areas being either marked on the roof surface or a roof plan. As a general rule reading below 40% are considered as a 'dry' construction. Readings between 40-60% may be classed as part of the construction being 'damp' and readings over 60% classed as part of the construction being 'wet'. In any damp or wet areas the exposed accessible flat area of the waterproofing membrane on the roof is visually inspected and the site formed laps physically tested with a lap scribe to identify pathways through the flat area of the waterproofing membrane and into the construction.

It is important that the results are correctly interpreted as incorrect interpretation could lead to unnecessary remedial works at great expense. Used correctly capacitance surveys can be an invaluable tool in determining the condition of a roof.

Electrical Capacitance Testing - Contact us now for more information or to request a brochure.