Cavity drain membranes provide an alternative to conventional cementitious 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 lose 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.