Cavity Drain Systems and Cementious Tanking for Basement Waterproofing
There are two forms of dealing with below ground waterproofing. Both systems carry a 10 year guarantee. A cavity drain method which involves using a high density studded plastic waterproof membrane which acts as a dry lining to ceiling walls and floors. There is an air gap behind which allows water movement which is channelled into a drainage system which in turn drains to a sump pump with non return valves and then can be drained away from the building.
The membrane is fixed using waterproofed plugs and all joints are sealed using a waterproofed tape. The internal finishes to the membrane can be sand and cement rendered and left or finish plaster can also be applied. The most common finish is to dry line with plaster board and the floor either boarded or screed finished. The alternative to cavity drain system is to prepare substrate, apply a water proofed 3-1 mix 10mm sand and cement render followed by a cementious wall tanking coat which is trowel applied followed by a further 10mm waterproofed render coat. This in turn can be finish plastered if desired.
Basement Penetrating Damp
Basement areas and retaining walls are particularly prone to penetrating damp due to increased water pressures at sub-ground levels. In most cases below ground moisture will penetrate through up to ground level, therefore all plaster and backing coats will need to be removed up to the DPC level and treated for moisture ingress.
Cementious Tanking Systems; involve applying two coats of waterproof sand and cement render onto prepared brickwork or block work. Then applying a cementious waterproof tanking mix over the render followed with a further coat of waterproof render. When dry, the area can be finished with plaster if necessary.
Cavity drain membranes; provide an alternative to conventional cementious tanking systems, which work by holding the water back. Cavity drain membranes work on the principle of allowing water to continue to penetrate the structure but control it in the air gap and divert it to a suitable drainage point. They do not allow pressure to build up against the internal construction and the air gap behind the membrane allows the structure to breathe and to some extent to dry out.
The membranes are loosely laid on floors and fixed to walls using special plugs and sealing materials, with little or no preparation required to the substrate. Once the membrane has been fitted, wall surfaces can be dry lined or plastered directly and floors can be screeded or a floating dry board system installed.
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