The Validator will identify areas of defects in the manufacturing of the membrane i.e. delamination, holes, tears etc. After installation, check for burning of the membrane during welding procedure which causes holes in the jointed seams also for any large stones, objects under the membrane which could cause damage during concrete flooring procedure.

Review of the installers relevant qualifications/training certs (i.e. CSCS cards or NVQ certificates, as applicable)

Phoenix Geotechnical Ltd will enter into a contract  as a third party independent validator for the ground gas membrane works at the Project/Site.

Verification Plans will explain how Phoenix Geotechnical will verify the ground gas membrane works. Phoenix Geotechnical will produce a Validation report for the buildings/units once the verification is complete. The validation report will be for the installation of the ground gas membrane works carried out. Phoenix Geotechnical will refer to the our clients Method Statement for the specification of the ground gas protection measures and installation procedures for specific projects.

D4437:- Nondestructive Test Method, Air Lance Test

We inspect all seams for un-bonded areas using an air nozzle directed on the upper seam edge and surface to detect loose edges, riffles are indicating unboned areas within the seam, or other undesirable seam conditions.

Checking all bonded seams using a minimum 50psi air supply directed through a 4.8mm nozzle held not more than 51mm from the seam edge and directed at the seam edge.

Air Lancing (non-destructive ASTM D4437) method used to check all areas where possible, welded joints of the Ground Gas membrane and GRSAM for all penetrations i.e. Steel Stanchions, pipe entries etc.

A Mechanical point stress test will be used where Air lancing is not possible.

Verification Plans and Reports

Phoenix Geotechnical verification plans and reports are prepared in accordance with the best available practice and the relevant guidance documents listed below:

Chartered Institute of Environmental Health (2008). The local authority guide to ground gas.

Wilson S, Oliver S, Mallett H, Hutching H and Card G (2007) Assessing risks posed by hazardous ground gases to buildings. CIRIA Report C665.

CIRIA Report C735 (Good Practice on the Testing and Verification of Protection Systems for Buildings Against Hazardous Ground Gases) and ASTM Standards D4437

CIRIA C748 (2014) Guidance on the Use of Plastic Membranes as VOC Vapour Barriers

CIRIA C795 Retrofitting hazardous ground gas protection measures in existing or refurbished buildings

BRE 414 and 212

BS8485 2015 and A1:2019

High Voltage Test Equipment

Phoenix 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.


Phoenix 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.


There 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:


Method 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.


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