Waterproofing systems

In the domestic market, cavity drain systems seem to be growing considerably in popularity, and probably at the expense of multi-coat render systems.

The following waterproofing methods are described below:

• cavity drain – Type C;
• multi-coat render – Type A;
• cementitious coatings –Type A;
• liquid applied membranes – Type A;
• mastic asphalt systems – Type A; and
• bonded sheet membranes – Type A.

It is no doubt possible to design in (using inner walls or linings) a drained cavity to work in combination with any of the above waterproofing materials.

When devising remediation of basement dampness, a waterproofing system needs to be selected, carefully considering at least the following criteria:

• ability to cope with hydrostatic pressure;
• loss of internal space (loss in room width and ceiling height);
• requirement for sound substrate (e.g. for good bonding);
• extent of substrate preparation required;
• ease of application;
• provision for post-installation fixings (for services, joinery, etc.);
• decorative options available;
• ease of repair/maintenance; and
• value for money (e.g. cost versus expected life and performance of system).

Reputable systems are designed to meet current building regulations, be supported by BBA certification, and be installed by trained operatives. The selected system should be supported by an insurance-backed guarantee, although the honesty, reliability and professionalism of a reputable contractor will always be your most important 'guarantee'. Any system must also enable the required grade of basement to be achieved. Systems selected must meet Health and Safety and COSHH (Control of Substances Hazardous to Health) requirements.

The selection criteria listed could be extended to help you make optimal decisions for particular contracts.

• It may be necessary to install waterproofing using methods that minimise disruption, dust or noise.
• Hacking off hard renders can cause untold damage to a substrate, especially a softish brick or stone, and sometimes walls will have been very seriously damaged from multiple hackings-off of renders from repeated attempts to damp-proof/waterproof over the years.
• Perhaps there are time constraints and the quickest methods must be used.
• In historic buildings you may need to install waterproofing that causes least damage to existing building fabric, or could be removed at a later date (i.e. is reversible). Any hacking-off of stubborn finishes that damages underlying substrate might be deemed unacceptable for a valued historic property.

Producing a dry living space from a previously damp and wet cellar really asks questions of designer and contractor – there is no place to hide. This is why you need to employ the best waterproofing contractor you can find. Remember that remedial waterproofing is not considered by the remedial damp-proofing industry to be very long-lasting – an expected life of 20–30 years is suggested in the BWPDA Code of Practice. Bear in mind too that remedial treatment contractors so often only provide a 10-year guarantee.

Waterproofing needs to be installed near perfectly, and remain near perfect, to keep water out over the years.