Necoseal - Radon Barrier Membrane

Necoseal - Radon Barrier Membrane

Monarflex® Necoseal is part of the Necoflex RAM™ - Radon, Air and Moisture Protection System, and when correctly installed and detailed in the floor construction protects the structure and occupants by providing an effective barrier to the passage of radon gas, air and moisture into the building from the underlying soil.

It is a loose-laid radon barrier membrane and may be installed below or above a ground-bearing slab, or on top of a suspended concrete floor. Monarflex® Necoseal is also suitable for use as a damp-proof membrane.

Features & Benefits

  • High elongation at break
  • High resistance to tearing
  • Joints and seals easily
  • High water vapour resistance
  • High radon gas resistance
  • Enhances overall air tightness of building.

Product Availability

Monarflex® Necoseal is manufactured from a single film of virgin low-density polyethylene (LDPE) to a thickness of 0.3 mm. The The membrane is black and has the words Necoseal Radon – Air – Moisture printed on the surface.

Product Code Description Roll Size Weight
3006659 Monarflex Necoseal 4m x 20m 22kg


Product Data and Performance

Product Data
Width: 4.0m
Length: 20m
Colour: Black
Weight/unit area: 280 g/m-2
Membrane Thickness: 0.3mm
Water Vapour Resistance 990 MN·s·g-1
Equivalent air thickness: Sd = 178 m


Considerations: Installation of Monarflex® radon resisting membranes must be in accordance with the recommendations of ‘IS 325: Part 2:1995’ and ‘BS 8102: 1990’. Additional guidance on the use of damp proof membrane materials is given in ‘BS 8000:Part 4:1989 Workmanship on building sites - Code of practice for waterproofing’.

The integrity of a radon resisting membrane must be maintained during installation. Monarflex® Necoseal is one of several Monarflex® Radon Resisting Membranes available. They have varying degrees of resistance to puncture and tearing. Specific guidance on membrane selection is contained in NSAI Agrement Certificate 09/0328. 

Durability: Monarflex® Necoseal is manufactured to last the lifetime of the construction provided it is correctly installed and not damaged by subsequent building operations.

Compatibility: Monarflex® Necoseal membranes are fully compatible with the range of Icopal damp-proof courses and membranes. 

Installation Details

Jointing: To form joints between adjacent sheets of Monarflex® Necoseal lap the membrane by a minimum of 150mm and seal with a strip of 30 mm wide Necobond or Monobond RT™ tape.

Ground Bearing Slabs: Monarflex® Necoseal may be laid over or beneath the concrete slab. When laid below slab Monarflex® Necoseal should be placed on top of a gas permeable layer, such as hard-core blinded with well compacted sand. When placed above slab, the surface should be smooth and free from any projections which may damage the membrane. Monarflex® Necoseal should then be covered with a screed or other suitable protective layer.

Suspended Floors: Monarflex® Necoseal should be laid over the floor slab and then covered with a screed or other suitable protective layer.

Monarflex® Necoseal radon barrier membrane should be installed and fixed in accordance with the manufacturer’s instructions.

Application: Where service ducts or pipes penetrate the membrane, joints are effected using Monobond RT™ sealant tape and top hat units with retention clips. Alternatively, the Easi-Pour™ self-levelling liquid sealant may be utilised.

Complex junctions around penetrations such as, steel stanchions and concrete columns may be detailed and sealed by using a fully bonded membrane such as Xtra-Load® GRM or Easi-Flash® self adhesive, bituminous membranes with an overlap of 150mm on each surface.

Detailing work should ideally be completed first to limit foot traffic across the membrane. Once completed, Monarflex® Necoseal may be laid and overlapped and sealed with Necobond™ or Monobond RT™ sealant tape. The membrane should be rolled down firmly to ensure an effective bond and seal.

Steel, concrete and masonry surfaces should be primed with Xtra-Seal® QD Bitumen Primer prior to the application of the fully bonded membrane.

Repair: Any damage must be repaired using patches of Monarflex® Necoseal, extending a minimum 150mm from the puncture and continuously sealed with Necobond or Monobond RT™ sealant tape.

Quality Assurance

Monarflex NecoSeal is manufactured under a Quality Management System approved to ISO 9001: 2000 by BSI Quality Assurance.

    Contact Icopal 0161 8654444

    Find Local Support

    To discuss your project in more detail please contact
    Your Local Area Manager


    Technical Support


    0330 123 4585



    Sales Enquiries & Orders


    0843 224 7400


    0843 224 7401


    Latest News

    A new faster, safer, stronger and lighter metal tile solution from BMI


    Band of Builders and BMI team up for community project


    The search is on for the BMI Apprentice of the Year 2020


    Oscar heads for the limelight


    BMI helps Children in Need keep young people safe


    Everyone's a winner - that's the truth!


    This site uses cookies in accordance with our Website Privacy Policy. By continuing to browse the site you are agreeing to our use of cookies. To browse without the use of cookies, you can opt-out as explained in our Website Privacy Policy or adjust your cookie settings for your browser

    Icopal: We Protect Your Building