Gas-Resistant Waterproof Membrane


Combi-Seal is a cross-laminated, lightweight, pre-applied membrane which will resist ground gases and water. The membrane utilises PREMCRETE APAN™ technology to produce a membrane which will effectively resist water pressure and gases from within the ground. The polyethene component is reinforced with an aluminium core to restrict gas vapour transmission to less than 40ml/day/M² in accordance with BS 8485:2015 + A1:2019.

The active nature of the membrane secures its integrity of the membrane whilst the textured profile of the membrane ensures an integral bond to the structure to which it is applied. Combi-Seal fully complies with BS 8485:2015 + A1:2019 for the protection against ground gases including carbon dioxide, radon and methane. It also complies with BS 8102:2022 for the protection of substructures against groundwater.


Combi-Seal is used as a pre-applied gas-resistant waterproofing membrane for basement construction, lift pits, concrete retaining walls and other structures which extend below ground where resistance to both ground gas and water is required. COMBI-SEAL may also be used to protect ground floor slabs, particularly where a good mechanical bond is required to the underside of the concrete slab or where a clay heave-board has been installed. Combi-Seal achieves 2 points when correctly installed in accordance with Table 7 of BS 8485:2015 + A1:2019.

Next Steps

Share Product


  • Combined Gas and Water Resistance
  • Lightweight but robust membrane.
  • High tear resistance.
  • APAN™ technology.
  • Forms strong adhesive bond to freshly placed concrete.

Related Case Studies

Civic Campus Scheme
Whittington Hospital
Bam Construction
Old Kent Road, London
Malt Street
Berkeley Homes