Cavity drainage membranes are used to waterproof walls and floors below ground levels, and also vaulted construction. The systems work by lining the areas to be protected with the appropriate membrane on the internal surfaces. All membranes joints and fixings are sealed, using specialised sealing products to prevent any ingress of water or moisture. The systems can also be used as protection against contaminants such as salts, carbon deposits, fertilisers, oil etc.
Because it is not possible to determine the amount of potential water pressure surrounding the structure, BS8102 tells the designer to expect a head of water to ¾ the depth of the structure for a structure up to 4m below the ground, and that for deeper structures, a head of water to 1m below the depth of the structure.

You may have considered ‘Tanking’ as a method of waterproofing the structure. Tanking, classified as ‘Type A’ waterproofing by BS8102 is basically the insertion of a barrier to either the inside or the outside of the structure that is designed to hold back the expected water pressure.
Because it is dependant on holding back what can be significant water pressure, a Tanking system has to be completely defect free for it to be successful. In the court case Thomas Wetherald V Outwing Construction, the court ruled that it is not possible for the tanking to be 100% defect free, and it was recommended that Tanking should not be used on its own as the only means of waterproofing.

Structures are very strong in compression but relatively weak in tension. The lateral bending stress imposed by water pressure can force through joins and can cause tanking to crack and fail. System 500 does not impose these stresses on the substrate. Unless the structure is designed by an engineer to withstand the stresses imposed when tanking withstands water pressure tanking should not be used. Even if the Tanking where to be successful, a hairline crack in the structure due to movement caused by vibration or thermal contraction or expansion is enough to crack or delaminate the Tanking leading to failure. System 500 is not affected by structural movement and its resulting cracking.

Installing water proof renders and slurries is another form of tanking. This form of tanking is prone to cracking and debonding.
The preparation has to be perfect and is not easily achievable to a required standard. Any vibration or movement will lead to cracking or de bonding. A correctly specified and applied render or slurry system would be far more expensive than a Membrane system but with none of the advantages.

The MACLENNAN-LSE WATERPROOFING system will conform to BS8102:1990 Protection of Structures Against Water from the Ground, and is termed as Type C Drained Protection. Our method of waterproofing is used on a daily basis to waterproof both new build and existing structures, and is used extensively to waterproof structures where Tanking has failed. Because water will ingress at the weakest point in the structure, MACLENNAN-LSE WATERPROOFING System 8 places depressurisation air spaces to intercept the water that may leak into the structure through the junction between wall and floor utilising the wall floor junction drainage channels. It is a condition of insurance companies that the plastic channels are used and for good reason. Water will almost certainly only ingress through defective joins in the wall floor junctions, floor slab joins or defects in existing masonry. Water should be picked up at these points by the plastic drainage rather than cross concrete to drainage. Water running over new concrete picks up free lime and when it dries calcification can occur which eventually causes blockages. Drainage channels should always be accessible and serviceable.