Guide Notes

Electronic integrity testing of waterproofing membranes and systems

Scope

This guide relates to methods of electronic testing to newly installed roof systems with continuous waterproof coverings, as well as structural concrete with flexible waterproofing, such as roofing felt, mastic asphalt, single-ply membranes and liquid-applied coatings. It does not include rigid systems, such as roof tiles or exposed profiled metal roofs.

The guide is intended to provide those involved in the design, installation and management of such waterproofing systems with the necessary information to ensure quality in the selection and execution of integrity testing services.

Test methods

Two methods are described here, the selection of which depends on the build-up of the waterproofing and weather conditions:

  • Low voltage (wet)
  • High voltage dry

Both rely on the electrical insulating characteristics of the waterproofing and conductive properties of the deck on which it has been applied.

Objective of testing

The objective is to determine the integrity of the installed waterproofing system as a whole, rather than any single component.

Electronic testing has to be distinguished from those that detect entrapped moisture or insulation defects, such as infra-red or electric discharge.

Low voltage – Wet

Also referred to as Electrical Conductance, Earth Leakage test.

Uses low-voltage direct current to create an electric field across the wet surface of the waterproof covering. Any breaches in the membrane alter the electric field and, as current is directional, it can be detected and traced back to source.

A loop conductor is placed on the membrane to define the area of test and to exclude extraneous signals from earthed details and structural elements (e.g. smoke vents or plant support rails), which would otherwise distort the results.

The operative uses a meter to detect changes in the field caused by electrical leakage to earth at points of potential water leakage.

Applications

  • Accurate location of points of electrical leakage to earth through the waterproofing, which are actual or potential sources of water ingress
  • Can be used on upstands close to the point of termination to the structure.
  • Well suited to virtually all types of waterproofing membrane systems.

Requirements

The waterproof membrane must be an electrical insulator. A continuous electrical earth, or representation thereof, must be present below the waterproof system.  This may be an electrically conductive deck, foil-faced insulation, or a foil-faced vapour control layer.

A newly installed membrane or system must have been exposed to a period of rainfall or soaking as described prior to test.

The membrane surface must be thoroughly wetted in the area under test and remain so for the duration of the testing.  A water supply to the area of test is thus essential.

Limitations

  • May not be fully effective on inverted, ballasted, paved or planted roofs, in which case the coverings should be set aside (existing roofs) or tested prior to overlay.
  • Not applicable on EPDM membranes or foil-faced bitumen membranes as these are electrically conductive
  • May also be ineffective on aluminised painted surfaces.
  • Not usually effective with timber panel decks such as plywood, which do not present as electrically conductive.
  • May be ineffective on some insulated systems, due to water not being able to pass through to electric earth
  • Not to undertaken on frosted or icy surfaces.

Efficacy of test

This depends upon:

  • the experience of the operator
  • the proper functioning and calibration of the equipment
  • prior knowledge of the roofing specification and the structural support.

Prior to integrity testing a new installation, it is essential that it has been exposed to sufficient water that would have passed through any breaches in the membrane and made contact with electric earth.  Without it, the test could be ineffective, at least in part.  Wetting can be achieved by exposure to rain for a period of hours or days or a defined period of artificial watering, into which a surfactant has been incorporated.

All new installations should be tested as soon as practical upon completion, following which it should be protected against damage.   If there is any delay before final handover or the laying of permanent coverings, with the risk of damage, a second test is strongly recommended.

High Voltage – Dry

Also referred to as holiday test/ electric discharge test

Uses high voltage (safely, due to very low current) to detect points of electrical discharge to earth through the waterproof membrane.

This is a contact method, whereby a copper or other metal brush is connected to a portable high voltage generator (10-20KV nominal) and swept across the membrane surface. Breaches are detected by a significant drop in voltage and a corresponding audible warning.

Applications

  • Accurate location of points of electrical leakage to earth through the waterproofing, which are actual or potential sources of water ingress
  • Can be used on upstands close to the point of termination to the structure.
  • Best suited to liquid applied membranes, such as bridge deck waterproofing (but not water-based coatings)
  • Can be used effectively on single-ply membranes

Requirements

  • Membrane must be dry
  • Built-up systems must have been exposed to sufficient water to seek out breaches, then dried thoroughly prior to test
  • Discharge voltage must be accurately set to ensure detection of pinholes or other breaches without burning the membrane
  • Residence time on the surface must be limited be continual movement of the brush until a breach is detected and recorded
  • As this is a contact method, the area of test must be clear of all materials and equipment.

Limitations

  • Not applicable on EPDM membranes or foil-faced bitumen membranes as these are electrically conductive
  • May also be ineffective on aluminised painted surfaces.
  • Not usually effective with timber panel decks such as plywood, which do not present as electrically conductive.
  • May be ineffective on some insulated systems, due to water not being able to pass through to electric earth
  • Not to undertaken on frosted or icy surfaces.

Complementary visual inspection and testing of seams

The test methods described above should be complemented by close visual inspection of all seams – especially at details – and by manual testing of a proportion of field seams using a suitable probe.

This inspection may be carried out by the roofing contractor, membrane manufacturer or test service provider, but it is recommended that the party responsible be identified in the contract documents.

The contractor must be able to repair immediately any breaches or other defects identified during test

Health & Safety

Prior to commencement, the test service provider must submit a Risk Assessment for approval.

None of the methods described presents a significant health and safety risk in respect of the electrical output. Nonetheless, care is required with the ‘Dry’ (high voltage) method.

Normal health and safety procedures must be adopted, particularly relating to work at heights.

Some membranes may be slippery when wet, especially if detergent is used during testing.

Testing must not be carried out in frost, snow, heavy rain or high wind, unless deemed safe to do so by the Employer and service provider.