Flat Roof Waterproofing
Liquid roof waterproofing systems offer a versatile range of options.Liquid-applied waterproofing systems are either based on natural bitumen, artificial polyester or polyurethane. They are typically used for the remedial covering of existing flat and pitched roofs, and their advantage is that they can be applied without removing the existing roof covering.
They can also be used for new roofs. Systems that can withstand heavy traffic may be specified for balcony surfaces and walkways. Expected service lives vary from between five and 30 years.
Typically, systems include a primer, layers of the waterproofing liquid, a reinforcing fibre layer and a protective top layer. Systems may comprise one or several coats. Coloured systems will fade with exposure to light. Waterproofing systems are predominantly based on three materials, bitumen, polyester and polyurethane, as detailed below. Other liquid-applied waterproofing systems include formulations based on rubber, acrylics and silicones.
Modified bitumen
Bitumen is modified by substances such as natural rubber or styrene to make it more resistant to fatigue movement failure. Two or more bitumen solution or emulsion layers are applied to a total thickness of 3-6 mm or greater. Expected service lives vary between 10 and 20 years.
Polyester-based systems
These are glass-reinforced fibre systems. "Resilient" types are applied to plywood or similar substrate. "Flexible" types are applied to existing substrates. The system is 2-3 mm thick. Expected service lives are between 20 and 30 years.
Polyurethane-based systems
Some polyurethane systems may be more tolerant of moist laying conditions. Thickness of system is 0.6-2 mm. Expected service lives are between 10-25 years.
Central to the long-term success of liquid-applied waterproofing systems is preparation of the substrate and achieving the required membrane thickness.
Typically, manufacturers only guarantee their products when applied by approved and trained installers. This is not surprising as standards of application by squeegee, roller, brush or spray are very demanding; layers are measured to tenths of a millimetre and avoidance of air holes is essential. The weather conditions in which the liquid is laid are critical as are the times between application of coats
