Wykamol CM8 Geotextile External Drainage Membrane (8mm Stud)

Design Considerations:

• Build new structures to the requirements of BS 8102:2009. Further guidance is available in CIRIA Report 139 - Water Resisting Basements.

• Use Waterbars at construction joints as part of an effective multi-staged approach to the waterproofing.

• Carry out a geotechnical survey to evaluate soil characteristics and groundwater conditions in accordance with BS 8004. Great care should be taken when considering waterproofing that requires the permanent removal of the ground water to be effective. See BS 8102:2009 Section 5 for further guidance.

• When used as a drainage membrane, Wykamol CM8 Geotextile Membrane should only be used to sloping sites where ground water is diverted around and drained away safely downhill of the structure.

• The land drain or perforated pipe to the base of an externally applied drainage membrane should be maintainable and graded to an open outlet below the level of the lowest slab. If risk of surcharge exists a pumped back flow protection device should be used. See BS 8102:2009 Section 6.4 for further information.

• Land drains or perforated pipes should be maintainable. Include accessible jetting ports at regular intervals with at least one jetting port to each elevation.

Substrate Preparation:

Prior to application of Wykamol CM8 Geotextile Membrane, consideration needs to be given to the soil composition and at what depth the water table is. We would recommend this investigation be carried out by a Geotechnical Engineer to determine the potential risks.

Ensure all surfaces are free from any sharp protrusions and in reasonably sound condition. Using Universal Mortar, provide a triangular mortar fillet at any point of the wall where it is necessary to smooth out angles between the vertical and horizontal elements of the structure.

Installation - Vertical Surfaces:

Apply a suitable Liquid Applied Waterproofing Membrane to walls in accordance with the product data sheets. If the Liquid Waterproof has been applied below the raft, link the raft and wall membrane to provide continuous waterproofing.

Apply Wykamol CM8 Geotextile Membrane horizontally. The membrane is held to the wall by the back-fill. Do not use fixings through the drainage layer as this will also perforate the waterproofing membrane. Use Wykamol CM Brick Plugs as a final fix to the top of the installation ensuring that this is above external ground level. Using temporary means to hold the membrane in place whilst backfilling, overlap subsequent sheets of Wykamol CM8 Geotextile Membrane, ensuring that the filter fabric of the next sheet overlaps the previous studded core - a section of filter fabric is separated from the drainage core for this purpose.

Seal the edges of sheets using the flange at the edge of each sheet using Wykamol Membrane Tape or Wykamol Corner Strip Tape.

Place a slotted drain to the base of the foundation so that the top of the drain is below the top of the internal slab level. Place the drain within a bed of clean graded 20mm stone surrounded by a sheet of Geotextile filter fabric ensuring that enough Geotextile is available to lap to the Wykamol CM8 Geotextile Membrane to give continuity of the filter fabric.

NOTE: If Wykamol CM8 Geotextile Membrane is used below the raft also, the slotted pipe will need to be lowered so it is below the horizontal membrane.

Ensure the slotted pipe drains freely to a safe collection point that is downhill of the structure.

Place the Geotex filter fabric to the face of the membrane so that it is held in place by the back-fill.

Use Newton GeoStrip Capping Profile to the top edge of the membrane to prevent debris and back-fill from entering the cavity between the drainage core and the filter fabric

Carefully back-fill the excavation. If graded stone is used, a protection board is not required but the stone should be placed in controlled layers of no more than 600mm so as to prevent slump to the membrane. If the removed soil is re-used, ensure that it does not contain sharp stones and ensure that the soil is compacted every 600mm. If sharp stones exist within the re-used soil a protection board will be required.

Installation - Under the Concrete Raft:

Lay Wykamol CM8 Geotextile Membrane in adjoining strips above the hard-core. Sand blinding is not required. Extend Wykamol CM8 Geotextile Membrane past the footprint of the raft by 500mm and continue to the slotted drain surrounded in clean graded stone. Overlap and tape sheets with Wykamol Membrane Tape.

The Liquid Waterproofing Membrane should be laid above the Wykamol CM8 Geotextile Membrane as the primary waterproofing membrane, prior to the placing of the concrete raft.

Limitations:

Wykamol CM8 Geotextile Membrane is a drainage membrane, not a waterproofing membrane. Waterproofing of the structure should be achieved with a High Quality Primary Liquid Waterproofing Membrane.

Wykamol CM8 Geotextile Membrane should not be used to de-water permanently high water levels. See BS 8102:2009 Section 5 for further guidance.

Backfill should be compacted every 600mm to prevent linear shear of the filter fabric from the drainage core if no protection board is used

Do not fix through the waterproofing membrane to fix the drainage membrane.

Finishing:

We advise that the drainage pipes are checked to ensure they will carry water away from the footings either passively (taking advantage of natural gradients) or actively, using a sump and pump.

Pipes should have a jetting detail so pipework can be flushed at regular intervals.

Back-filling should be carried out with care to minimise the risk of physical damage to the membrane and prevent tears around the fixings.

Technical Data Sheet:

Declaration of Performance (DoP):

BBA Certificate