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Underground TankingLift Pits

Underground Tanking


Underground Tanking refers to the application of multiple layers of Derbigum waterproofing membranes to prevent the ingress of water under hydrostatic pressure.


Concrete walls are to be smooth off-shutter (board-joints rubbed smooth and ferrule holes filled) and to be free of voids and honeycombing. Care is to be taken to remove shutter release oils and all remnants of curing compounds. The concrete is to be cured and dry - generally accepted as when the bituminous prime coat achieves full adhesion. Brickwork is to be dry and smooth either bagged or plastered so as to achieve a uniform finish free of voids and protrusions.
Concrete footings and bases are to be clean, dry and smooth. Internal corners to be coved.


Waterproofing to be one layer of Derbigum CG4 on one layer Derbigum CG3 waterproofing membrane, with 100mm side laps and 150mm end laps, sealed to primed surface by “torch-fusion”, to receive protection or drainage layer and compacted fill (elsewhere specified by engineer). Waterproofing to be installed by an Approved Derbigum Contractor.



The waterproofing membrane must be protected from damage during the backfill operation to prevent rubble, (bricks or other debris) from damaging the membrane particularly during compaction. This protection may be a brick skin, polystyrene, fibrecement or softboard (or a combination of these). Alternatively, a Delta HD polyethylene drainage layer, may be used which serves the dual purpose of both protection and hydrostatic pressure relief.

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