Liquid-Applied Roofing

Liquid-applied roofing, also called liquid-applied membrane (LAM) or fluid-applied roofing, is waterproofing delivered to the roof as a liquid that cures in place into a continuous, seamless, fully bonded membrane. It is used for whole roofs, for refurbishment over existing coverings, and especially for complex details, balconies, terraces and walkways.

Chemistries

• Polyurethane: single- or two-component; elastic and widely used for roofs and balconies.
• PMMA (polymethyl methacrylate): two-component resin cured by a peroxide catalyst; very fast cure, even near 0 C (32 F).
• Unsaturated polyester and GRP: glass-fibre reinforced resin laminates.
• Acrylic: water-based elastomeric coatings, common for restoration and cool roofs.
• Silicone: high-solids coatings with strong UV and ponding resistance.
• Bitumen-based and rubberised bitumen: cold emulsions and hot-melt systems.
• Polyurea and hybrid systems: spray-applied, fast-setting.

Reinforced systems

Many roof-grade liquids are "cold-applied reinforced" systems: a base coat is applied, a polyester fleece or glass mat is embedded while wet, and a top coat saturates it. This wet-on-wet method gives uniform thickness and crack-bridging. PMMA systems with fleece typically reach about 2.3 mm (90 mil).

Codes and standards

The IBC requires liquid-applied roofs to have a design slope of at least 1/4 in per 12 in (2%). In the UK the Liquid Roofing and Waterproofing Association (founded 1979) publishes guidance and training, including a code of practice for hot-melt systems.

Advantages

• no seams, laps or mechanical fixings
• self-flashing around penetrations and irregular shapes
• often cold-applied with no hot works
• can be applied over many existing roofs

Limitations

Thickness depends on the installer, so coverage rates must be checked; a common site method is to mark grid areas matching each container's coverage. Many products are sensitive to rain, humidity and temperature during curing, and substrate preparation and priming are critical.