Wet test ( Vector Mapping )
Finding defects in waterproof membranes
Working on a similar principle to the dry test , the purpose of the wet test is to find defects in a waterproof membrane , but it only requires a conductive material to be present in the roof build up and not directly below the waterproofing .
Based on a low voltage signal ( between 30v and 40v ) generated from a battery the test is non-destructive and will pick up defects between lapped materials . The area to be tested has to be thoroughly wetted down but should not have standing water present . A chain or wire is then passed round the area to be tested and connected to the signal generator ; the generator is earthed to a suitable part of the building to complete the circuit .
Utilising a pair of probes with a directional meter attached , the operative then proceeds to measure the resistance of the membrane inside the chain , the meter will indicate where the resistance is reduced and lead the engineer to the defect . Water is used to conduct the water around the roof surface and , like electricity , the water is trying to reach earth and will follow the path of least resistance .
Unlike the dry test , water can enter the lap or seam of welded material and will help the engineer to pick up failed welds . Defects can then be marked on the roof and then repaired on marked up and put on a plan to repair at a later date .
Low voltage testing will work on nearly all membranes apart from ones that conduct electricity ( such as EPDM ) or have no conductive material at any level ( such as top deck or timber decks ). All membranes should be lap scribed once the testing has been carried out . The wet test will allow nearly any thickness of membrane to be tested provided it has been wetted down properly .
The roof does have to be clear of decking , debris , materials and all finishes to allow the test to work effectively , the chain has to be in direct contact with the roof membrane .
ADVANTAGES
Summary
Working on a much wider variety of membrane and roof build ups gives wet testing a major advantage over dry testing , however it does need a skilled operator to get the best results .
On new builds the roof should be wetted down substantially over a period of time to create the leak pathways . The wet test is not weather dependent so less likely to be held up although some ply membranes will need a wetting agent applied to increase the surface tension of the water a prevent run off .
DISADVANTAGES
Not weather dependent . Cannot be standing water on the roof . This can lead to false earth pathways being detected .
Works on nearly all roof membranes , e . g . liquids , asphalt , RBMS , single ply .
Does not need a conductive surface directly below the membrane . Provided there is a conductive element in the build up , i . e . concrete or steel deck , foiled faced insulation or VCL .
Non-destructive testing .
Can detect lap defects .
Needs a constant supply of water to stop membrane drying .
Needs a skilled operator .
Outlets , detailing , and penetrations have to be removed from the chain potentially leaving untested areas of the membrane .
Slower than dry testing / less area tested in a day .
Does not work on EPDM , limited results on Topdeck . Will not work on roofs that have no conductive element . e . g . Timber deck , tissue PIR .