Roofing Kettle

A roofing kettle is a heated vessel used to melt solid asphalt (or, historically and in some markets, coal tar pitch) and keep it at the correct temperature for application. Kettles are central to hot-applied built-up roofing (BUR), where layers of felt are bonded with mopped or mechanically spread hot bitumen, and to some modified bitumen and waterproofing work.

Equipment

• Kettles or tankers, typically trailer-mounted, heated by propane or other fuel burners, with capacities sized to the job.
• Thermometers and thermostatic controls to monitor and limit temperature.
• Pumps and pipelines to move hot bitumen to the roof, or luggers and buckets for hand transport.
• Lids and lid-closing mechanisms to smother fires and reduce fumes.
• Mops and mechanical spreaders for application.

Temperature control

Correct temperature is essential to roof performance and safety. Industry guidance uses the equiviscous temperature (EVT), the temperature at which the bitumen reaches the viscosity suited to mopping or mechanical spreading, measured at the point of application. Guidance published through IIBEC includes:

• Asphalt has a minimum flash point of 500 °F (260 °C) under ASTM D312.
• Asphalt should not be heated above 550 °F (288 °C), nor within 25 °F (14 °C) of its flash point.
• Asphalt should not be held between 500 °F and 550 °F for more than about four hours.
• Kettles are typically run somewhat above EVT to allow for heat loss in transport.

Overheating can lower the asphalt's softening point ("drop-back"), changing its properties.

Hazards

• Burns from hot bitumen are a serious risk; workers wear long sleeves, gloves, boots and eye protection.
• Fire: kettles must be attended, placed away from buildings and combustibles, with extinguishers nearby.
• Fumes: US NIOSH has studied asphalt fume exposure among roofers; controls include keeping lids closed and avoiding excessive temperatures.
• Propane cylinders and lines must be handled safely.

Many jurisdictions regulate kettle placement, attendance and fuel storage through fire codes. The use of hot-applied systems has declined in some markets as cold-applied, self-adhered and single-ply systems have grown.