Waterproofing Membrane for basement Floors 20 sqm

CM20 2x10
Price excl. VAT
Price incl. VAT
(20 items in stock)

Use our Baseline 20 mm cavity drain membrane to waterproof basement floors. The cavity drain membrane can also be used on tunnel walls which have a high volume of water entering the tunnel walls.

What is a 20 mm Cavity Drain Membrane?

The cavity drain membrane is an HDPE barrier with 20 mm stand-off studs at 50 mm centres. The stand-off studs create a drainage space to contain water seepage. The cavity beneath the membrane has a volume of 14 litres per square metre. The large gap is ideal when tanking floors prone to constant moisture intrusion or high-water table levels.

Our 40 and 20 sqm tanking membranes are robust and durable. Baseline 20 membrane will last the design life of the building. HDPE is rot-proof and resistant to alkaline, bacteria and fungi. Use the membrane to waterproof basement floors and other below-ground bases that require a cavity drain system. 

How do you use 20 mm Cavity Drain Membranes to Waterproof Basement Floors?

Set out drainage channels. Fit sump chambers where necessary. Treat freshly laid concrete with an anti-lime sealer to prevent free lime from leaching. Lay the roll of the membrane as you would lay Lino. Overlap the joints using the 100 mm wide stud-free flanges or ensure the membrane is lapped by a minimum of 3 studs. Use waterproof tape to seal all joints and floor-to-wall junctions. Finish with a concrete pour or a 65 mm screed.

Type C Waterproofing with Cavity Drain Systems.

Basement waterproofing membranes form part of a sealed cavity drain tanking system. The system must manage and dispose of water behind the membrane as per BS 8102:2022. Our Baseline 20 mm cavity drain membranes are BBA approved for Type C waterproofing.

We stock the Baseline 20mm waterproofing membrane in 2 m x 10 m rolls. The membrane is easy to cut and trim using a sharp blade. Twistfix offers expert advice on all our cavity drain membranes. You can buy them online at low trade prices.

  Baseline 20 Cavity Drain Membrane   Data
  Material   HDPE
  Sheet Thickness   1mm
  Membrane Height   20mm
  Water Void Capacity   >14.61 l//m²
  Weight   1 Kg/m² 
  Water tightness at 60 kPa   >24 hours
  Working Temperature   -50°C to +80°C
  Softening Temperature   126°C
  Mean Compressive Strength   165 kN/m² 

Delivery options are only available for delivery to mainland UK (excluding Scottish Highlands, Scottish Islands, Channel Islands, Isle Of Man Northern Ireland and Eire). Delivery to Scottish Highlands, Scottish Islands, Channel Islands, Isle Of Man, Northern Ireland and Eire are limited to 20kg and are available at a Premium rate. Please contact us on or via our help line if delivery is required outside these areas. Alternatively select ‘World-wide Delivery’ and a member of our sales staff will contact you regarding your options and costs.


We offer for the mainland UK , as standard, a FREE delivery service on all orders having a value greater than £200.00 (excluding VAT). For orders having a value less than £200.00 (excluding VAT) a carriage fee of £8.50 + VAT will be levied. Goods will be sent by a national carrier on their 1-2 working day standard service. Customers must understand that delays can always happen while their order is with the courier, for this reason we can not guarantee your order will be with you next day.

It is important that the customer ensures that all the delivery details are correct and that the customer or someone acting for the customer is able to sign for the delivery. Twistfix accept no liability for failed deliveries as a result of incorrect delivery details or the absence of any authorised signatory. Twistfix will attempt delivery to the recipient between the hours of between 8am and 6pm. If no one is available to receive the delivery an attempt may be made to leave the item with a neighbour. Alternatively the carrier may return the item to the sorting office and leave a calling card at the recipient's address to advise of the attempted delivery. It is the responsibility of the customer to arrange to collect the item from the depot or to arrange re-delivery with the carrier. Further information regarding Delivery can be read at our Terms & Conditions.


Items returned and received in their original condition and packaging within 14 days of delivery will be accepted for exchange or refund subject to a 20% restocking fee. You will be responsible for the shipping costs incurred in returning the goods and should ensure the items are adequately insured while in transit to us. You should email to request to return items.

Where the goods are being returned because they are faulty or are not the goods that were ordered then, subject to the goods being returned in re-saleable condition, Twistfix will refund the cost of return shipping. Further information regarding Returns can be read at our Terms & Conditions.