Hot-Melt Rubberised Bitumen

Hot-melt rubberised bitumen, called hot rubberized asphalt in North America and simply "hot melt" in the UK, is a fluid-applied waterproofing made from bitumen modified with synthetic rubbers and fillers. It is supplied in blocks or cakes, melted in special double-jacketed oil-heated melters to control temperature, and spread with squeegees onto a primed concrete deck.

System

A typical hot-melt system is built in two layers with a reinforcing fabric, usually polyester, embedded between them, giving a seamless, fully bonded, thick membrane. A protection sheet is laid over it before insulation or overburden. Because the membrane is bonded to the deck, water cannot travel beneath it, which makes leaks easier to locate and limits damage.

Where it is used

Hot melt is designed to be buried. It is the classic membrane for:

• inverted (protected membrane) roofs on concrete decks
• podium decks, plazas and terraces over occupied space
• green and blue roofs
• zero-fall roofs, where third-party certified systems are permitted

UK warranty guidance for zero-fall roofs accepts BBA-certified liquid-applied or hot-melt systems approved for zero falls in an inverted build-up, and does not accept excess hot-melt material left around outlets that impedes drainage.

Codes of practice

In the UK the Liquid Roofing and Waterproofing Association publishes a Hot Melt Code of Practice, updated to reflect BS 6229:2025.

Considerations

• deck must be sound, clean, dry and primed; it is mostly used on concrete
• hot work requires fire precautions and trained operatives
• the membrane is not UV-stable and must be covered
• integrity testing, often electronic, is commonly carried out before overburden is placed