Basement / Cellar Waterproofing

What is Penetrating Damp ?

Waterproofing is necessary when Penetrating Damp (as opposed to Rising Damp) travels across or down masonry.

Where high ground or below ground areas (i.e. your basement / cellar) are affected your surveyor will inform you that these areas require a tanking system.

What are tanking systems ?

There are many methods of tanking and all are designed to deal with lateral penetration of moisture from high and below ground levels. They can be grouped into three categories:

Cement Based Tanking
Cavity Membrane Systems
Slurry Applied Coatings

Cement-based Water Proof Render (Tanking)
Water proof renders are one of the oldest methods of water proofing and have been used by the remedial industry for many years.

The application of multiple coats of a water proof render (using sand and cement incorporating a quality waterproofer) to a previously prepared surface is designed to stop water entering the tanked area. However there are many disadvantages:

Tanking with this method can cause condensation as the wall surfaces are cold and the ambient air is warm in normal living conditions.
The render is subject to salt attack from sulphates which attacks the cement and breaks it down over a period of time.
It is prone to cracking due to structural movement or even vibrations from heavy traffic in some cases.
It is very difficult to repair should a failure arise.
It is difficult to achieve fixing of skirting and heavier items, as the render can not be pierced and everything must be glued.
It creates water pressure, pushing the water to other areas such as your neighbours' property, and in some cases can cause sheets of render or floor sections to blow if the water pressure is not relieved with sump pumps - as the photo below shows.

Cavity Drained Membrane Systems

The Cavity Drained Membrane System is, as the name suggests, a polyethylene studded sheet which is fixed to the walls, floor or ceiling with specially designed plugs with fitted seals.

It creates a cavity between damp masonry and a new wall surface. The base of the wall carries a drain channel which normally runs to a sump pump or manhole, thus relieving water pressure.

The system can be either dry lined or plastered directly on to to achieve a smooth plastered finish. This method of tanking:

eliminates the risk of condensation associated with cement render tanking.
is not affected by structural movement or vibration from traffic.
manages the water pressure by allowing the water to drain away, eliminating the risk of pushing the water elsewhere.
can be repaired fairly easily should it fail.

Slurry Systems

These are often cement based, two part flexible coatings which come pre-packed in powder form. The surface must be prepared and a salt inhibitor applied. The slurry can then be mixed and applied by brush.

The system has the same disadvantages as the Water Proof Render system with the added problems of eroded or perished brick requiring special attention, and the high cost of the materials.