Vector Mapping Grid (VMG™) (required under membrane on Lightweight Structure)
The VMG™ is a specially selected stainless steel grid that serves as a patented conductive medium when used with roofing/waterproofing systems that incorporate Electric Field Vector Mapping (EFVM®) leak detection systems. The VMG™ is installed below the roofing/waterproofing membrane.
EFVM® is a low voltage test method that creates an electrical potential difference between a non-conductive membrane surface and a conductive substrate, which is earthed or grounded. By applying water on the membrane surface and using the water as a conductive medium, an electric field is created and a breach in the membrane creates a vector (ground fault connection). The EFVM® technician reads the electric flow traveling across the membrane mapping the breaches with pin point accuracy.
Advantages of the EFVM® testing system
- Exact pinpointing of membrane breaches
- Non-destructive to the membrane
- Can be performed on sloped structural decks
- Membrane defects can be repaired and retested without delay to the construction schedule
- Limited use of water required for the EFVM® test
- Eliminates unnecessary removal of the overburden to locate a membrane breach
- Membrane performance can be monitored during its lifespan through the overburden
Scope of use
Vector Mapping Grid (VMG™)
The VMG™ must be used if any of the following conditions exist:
- in warm roof assemblies that incorporate insulation under the roofing/waterproofing membrane.
- in assemblies that incorporate a non-conductive structural deck such as plywood, unreinforced concrete, hollow core concrete with mesh in topping slab or cellular lightweight concrete.
- when the existing waterproofing material or vapour barrier will emain in place.
- when the new waterproofing system includes a vapour barrier over the structural deck.
EFVM® is used to find defective workmanship and damage to the waterproofing membrane (caused during the construction phase). This then allows the applicator to repair the highlighted breaches on the spot and handover a watertight membrane.
EFVM® is an approved testing as stated by Waterproofing Membrane Association Incorporated Torch on Code of Practise.
EFVM® tests ALL membranes apart from Butyl rubber membranes because of the Carbon contained in the make up of the product. (carbon absorbs electricity, not an isolator).
New Zealand Building Code (NZBC)
The product will, if employed in accordance with the supplier's installation and maintenance requirements, assist with meeting the following provisions of the building code:
- Clause E2 External moisture: Performance E2.3.7(a)
The product meets the requirements set out in the following documents, or relevant parts of cited standards within the documents:
EFVM® complies with E2 by ensuring the integrity waterproofing membrane is installed in accordance with NZBC.
Waterproofing Membrane Association Incorporated Torch on Code of Practice
6.5 Testing There are two methods of testing the integrity of a torch-on membrane after installation, either flood testing or electronic field testing. In both cases, after the testing has been carried out a written report confirming the integrity of the membrane must be supplied to the Main Contractor.
6.5.2 Electronic Field Testing Electric field testing works by passing a controlled electric current through the membrane with either a thin water film applied over the membrane or a pre-installed non-obtrusive metal grid under the membrane being the conductive medium. Any point of electric current leakage will indicate the location of a fault in the membrane system. This testing must be carried out by a trained technician.
The product has and can make available the following additional evidence to support the above statements:
Non-Conductive - Plywood
EFVM® requires Vector Mesh Grid between the plywood substrate and the membrane and this allows an electrical connection to be created if there is a breach in the membrane on a plywood substrate.
Membrane Application to Non-Conductive substrate
Vector Mesh Grid Installation
- The Vector Grid is laced directly onto the plywood substrate.
- The Vector Grid must cover the total area that is to receive membrane. This includes parapets, plinths, up stands and gutters.
- The Vector Grid Must be terminated 50mm from membrane termination points, penetrations, outlets and projections.
- Vector Grid sheets must overlap at least one full square, at both edges and ends.
- The Vector Grid must be fixed with sufficient stainless steel staples to hold the grid against the substrate.
- The connection plate (supplied) must be securely clamped onto the edge of the Vector Grid at the location agreed by an ILD technician.
- A prefabricated cable (supplied) will be connected to the connection plate and terminated at a location agreed by an ILD technician.