Testing Dry Membranes

Screen Shot 2014-08-09 at 18.22.43Phoenix Geotechnical use high voltage test equipment and offer an aid for testing dry waterproof and gas membranes. Damage can be caused by tradesmen working in the area whether the structure is old or new.

The problem is to find the faults which can be the size of a pinhole and invisible to the naked eye.

Waterproof and gas membranes can be tested for pinholes and porosity by using a High Voltage Holiday Detector.

For the test to be effective, the membrane must have a conductive backing, i.e. PVC on steel, felt on concrete or foil-backed insulation board.

Faults through the membrane can be easily located by passing a high voltage across the surface using a brush or roller electrode.



Testing Dry Surfaces

membranePhoenix Geotechnical use test kits that have been used for many years to locate leaks in dry waterproof and gas membranes.

The PHD and PD Range of Pinhole/Holiday Detectors can be used to find faults in waterproof and gas membranes (non-conductive) with a great deal of success.

PD 130 Holiday Detector (PD30R)

– Recommended for waterproof and gas membranes as it can test thicknesses between 16 microns up to 14.4mm.



Testing Dry Waterproof and Gas Membranes

photo 2Principle of Operation

The earth lead from the PD/PHD unit is connected to a convenient earth point on the structure. A high voltage – calculated against the membrane thickness – is applied (using an electrode) to the dry surface of the membrane.

When there are no faults present the membrane acts as an insulator by stopping the flow of current out of the PD/PHD unit.

When the electrode passes over a fault or hole, the high voltage jumps the gap between the electrode and the water (or conductive layer) under the membrane, causing a current to flow. The audible and visual alarm on the PD/PHD unit will alert the operator, who can then mark up the points in need of repair.

Two types of electrodes are recommended for testing; a phosphor bronze brush for uneven surfaces, or a special roller for large smooth areas.



Criteria for successful testing

photo 5There are a number of criteria that need to be met for successful detection of membrane faults:

a) The test can only be carried out on waterproof or gas membranes which have a conductive substrate (aluminium foil, concrete, brick, steel or water etc).

b) The surface must be dry when the testing procedure is carried out. As water is a conductor of electricity, it would be impossible to find faults in a wet surface.

c) The membrane material must be able to withstand the test voltage – testing a sample laid on a sheet of metal would confirm this (see below).

d) The thickness of the waterproof and gas membrane must be known so that the test voltage can be calculated. Use the following formula to calculate the correct voltage:



Test Kit with Phosphor Bronze Brush Electrode

Complete line out (7)Testing a sample

A sample of material of uniform thickness (approximately 30cm square and less than 2mm thick) should be laid onto a metal sheet. Whilst the Pinhole/Holiday Detector is turned off, the test probe handle (fitted with a pointed probe electrode) and earth lead should be connected to the unit. The other end of the earth lead should be attached to the metal sheet.

With the output of the PD/PHD unit set at minimum to start with, the probe should be placed onto the membrane surface. The high voltage output should be turned on and slowly increased until the material beaks down and activates the alarm on the Holiday Detector, or the output reaches maximum.

The electrode should then be lifted off the surface and the output voltage shown on the PD/PHD unit which caused the material to break down should be noted.

The process should be repeated a number of times on new areas of the sample, allowing at least 20mm from any previously used areas, noting the “break-down” voltage each time.

A calculation should be made to find an average of the voltages. The Dielectric Strength of the material would be approximately 75% of the average of the voltages. If the material will not break down, the thickness of the membrane material should be reduced by half and the above processes repeated. The results obtained can vary from 8kV to 40kV per mm.

For a material to be tested using high voltage, its dielectric strength must be greater than 4kV per mm and preferably 8kV per mm. The greater the dielectric strength the less chance there is of making a fault during the testing process.



Testing Dry Waterproof and Gas Membranes

photo 1Method of testing

A suitable point on the structure should be identified as an earth connection for the earth lead of the Pinhole/Holiday Detector.

Following the instructions in the operating manual of the PD/PHD unit, the output voltage should be set according to the calculation made using the formula shown above. The earth lead and test probe handle should be connected to the PD/PHD unit whilst the unit is turned OFF.

The other end of the earth lead should be attached to the earth connection point of the structure ensuring that a good electrical contact has been made. 

With the PD/PHD unit still turned OFF, extension rods should be connected to the test probe handle. Using the shoe attachment, a suitable electrode should be attached to the opposite end of the extension rods. Any electrode used must be in good condition as a damaged one will not make full contact and faults could be missed.

The operation of the Pinhole/Holiday Detector should be checked by touching the electrode onto the substrate. The audible alarm should then be activated, but if not, the lead connections should all be checked. Sometimes it may be necessary to adjust the sensitivity control on the unit. Reducing the setting will make the unit more sensitive, while increasing the setting will make the unit less sensitive, i.e. for situations when the coating is damp.

The electrode should be passed slowly over the membrane surface at a maximum rate of 100mm per second, paying particular attention to edges, holes and irregularities in the coating. The test voltage may need to be reduced to test the edges as the coating may be thinner. 

When a fault is identified by the detector, the electrode should be moved sideways in order to identify the precise location of the problem. All faults should be ringed with a suitable marker so that repairs can be carried out at a later date. The identification of the fault should be far enough away from the defect to allow the repairs to be made without covering the markings, as the substances contained in some markers can affect the adhesion of the repair material.

Testing should be continued across the complete surface and all faults marked. Damaged areas should be re-tested after repairs have been carried out.



Contact

For more information please contact us on the below details:

T 01743 709192

[email protected]

 

8 DeQuincey Fields
Upton Manga
Shropshire
SY4 4US