Waterproofing systems

Liquid applied membranes are a potentially effective means to waterproof a basement.

Most surveyors will be familiar with Synthaprufe – the most common liquid applied waterproofing material. It is a strange liquid that is brown in the tin, turns black once applied, but then returns to brown if it fails. It is a bituminous emulsion containing natural rubber latex that dries to a waterproof and vapour resistant black flexible film. Synthaprufe is resistant to sulphates and other salts from the soil. Synthaprufe bonds well to other materials, but needs to be protected to ensure long life and effectiveness.

Synthaprufe can withstand 'normal building movement'. Once applied correctly, a seamless waterproof membrane is achieved, and it can be applied to damp surfaces – a great asset when waterproofing basements, for obvious reasons.

Synthaprufe is applied using a disposable brush, with coats applied to build up a finished thickness of minimum 1mm. But here lies a problem: on a surface that is not totally flat and uniform, it might be difficult to ascertain that the correct finished thickness has been applied over the whole area.

The manufacturers recommend that a floor waterproofed using Synthaprufe is covered by a 50mm 1:3 cement/sand screed. On walls, and in 'conditions of mild dampness' a 'finish of a minimum of 12mm of gypsum plaster should be applied before decorating'. In more severe conditions an inner loading skin of brick or block may be required. In conditions of hydrostatic pressure, or if it is to be used below ground or where anything more than 'mild dampness' is expected, the manufacturer should be consulted. Technical details are available from the manufacturer that show 3 coats of Synthaprufe used for tanking, protected by an inner wall of brick or block and a 50mm screed protection to the synthaprufed floor.

In BRE Good Repair Guide 23, a detail is shown of a liquid applied membrane used together with a blockwork loading wall and cement/sand screed topping. The BRE describe such a waterproofing option as 'durable', but with a 'space penalty'.

Other materials are used for liquid membranes, such as elastomeric urethanes or epoxies. Epoxies can be useful for floors as they can act as a vapour check and wearing coat when laid on a sound substrate.