Product Range - Radon Barrier Membranes - Necoflex

Xtra-Load GRM - Self Adhesive Gas Retardant Membrane

Xtra-Load GRM Gas Resistant Self Adhesive Tanking Membrane is a high performance, self-adhesive flexible cold applied waterproofing membrane for horizontal and vertical applications. When correctly specified, installed and fully protected will provide an effective barrier to water, water vapour and radon. Xtra-Seal GRM is compatible with concrete, smooth brick or blockwork and screeded substrates.

Features & Benefits

  • Ease of application.
  • Resistant to tearing.
  • Tested by National Radiological Protection Board (NRPB) for resistance against Radon.
  • Tested by Wimpey Environmental for resistance against Methane.
  • Compatible with all forms of DPM’s and DPC’s.
  • Joints and seals easily.
  • High water vapour resistance.

Product Availability

Xtra-Load GRM comprises of a bitumen/polymer, self-adhesive compound, aluminium foil and cross-laminated, high-density polyethylene carrier, with a white finish to the upper surface with a 50mm self adhesive bitumen selvedge with a pull off release film giving improved overlap security. The aluminium foil layer provides resistance to the passage of gasses such as methane, carbon dioxide and radon.  

Product Code Description Roll Size Roll Weight
3100407 Xtra-Load GRM Gas Resistant Self Adhesive
Tanking Membrane
19.05m x 1.05m 34kg


Product Data and Performance

Performance Data
Nominal Thickness: 1.0mm
Water Vapour Resistance: 892 MNsg-1


Durability: Xtra-Load® GRM, when fully protected and subjected to normal service conditions, will provide an effective barrier to the transmission of water and water vapour for the lifetime of the structure in which it is incorporated.

Compatibility: Xtra-Load® GRM is compatible with concrete, smooth brick and blockwork or screeded substrates, and are resistant to those chemicals with which they are likely to come into contact. However, care should be taken to prevent contact with mould oil and hydrocarbons.

Resistance To Puncture: Provided sharp objects are not present prior to and during installation of the protective layer, the membrane will not be damaged by normal foot traffic.

Resistance To Moisture: When completely sealed and consolidated Xtra-Load® GRM will meet Building Regulations requirements in the resistance of the passage of moisture from the ground. The membrane is impervious to water.

Loading: When these tanking membranes are fully confined they may be regarded as having the same compressive strength as the containing material, however when building masonry off the membrane, a dpc material should be installed over the membrane to act as a crushing layer and protect the membrane from point loading.

Installation Details

Xtra-Load® GRM must be installed in accordance with the requirements of 'BS 8102: Code of practice for protection of below ground structures against water from the ground' and 'BS 8000-0: 2014. Workmanship on construction sites. Introduction and general principles'. Tanking should be externally applied wherever possible and immediately protected.

Preparation Of Surface: All surfaces should have a smooth finish, free from cavities, projections and mortar deposits. Surfaces should be dry and free from dust and frost. Concrete surfaces should be dense.
Vertical surfaces of brick and blockwork should be dry and rendered to provide an even surface. Brick or blockwork not rendered must be flush pointed to give a smooth surface without sudden changes in level.

Priming: Prior to application of the tanking membrane, a priming coat of Icopal SA Bitumen Primer must be applied to all surfaces and allowed to dry.

Angles And Corners: Where the horizontal surface meets the vertical surface, a 50 mm by 50 mm fillet should be used, reinforced with a strip of membrane. Reinforcing angles are formed by cutting a 300 mm strip of Xtra-Load® GRM from the roll.

Application: The ideal application temperature range is 5°C to 35°C. At low temperatures the products will become progressively stiffer, which may make it difficult to handle. The membrane rolls should be left in a heated storage area until immediately before application.

The tanking membrane should be applied only when atmospheric and substrate temperatures are greater than 5 °C. The surface of the substrate should be clean and dry and must be 3 °C above the dew point. If the surface is below or at dew point temperature then moisture can form at the surface and affect membrane adhesion.

Apply Icopal SA Bitumen Primer by brush or roller and leave until dry (approx 45 minutes to 1 hour, depending on weather conditions). The release paper should be removed in a continuous strip for the first 500 mm of the roll and the membrane pressed firmly into position to ensure no air pockets are formed.

Xtra-Load® GRM self-adhesive tanking membrane is supplied with a selvedge. Align adjacent rolls of Xtra-Load® GRM tacky side down, allowing a side overlap of 50 mm and end overlaps of 100 mm. Peel back the release paper and the selvedge as laying progresses. Press down roll joints firmly to develop and immediately bond, and to ensure a water-tight seal. The use of a hand roller will aid in providing a firm seal.

Vertical work: The membrane should be applied starting at the top of the section of vertical wall. Using the action of gravity to aid installation, the backing sheet should be removed and the membrane well rollered down working from the middle to the edges to remove any pockets of air and to ensure a full bond to the substrate.

Membrane Protection: On completion, the tanking membrane must be immediately protected following a detailed inspection for damage and faults. To ensure Xtra-Load® GRM is not damaged during backfilling or by following trades, a screed, or non-rot protection board, such as the Xtra-Load® Protection Board, should be laid immediately following application. 

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