Tech Today

How hot is hot?

You most likely realize properly heating asphalt in kettles or tankers and proper asphalt temperature at the point of application are important for constructing hot-applied built-up and mop-applied polymer-modified bitumen membrane roof systems. However, what you may not realize is these values are changing for specific asphalts in ways that may limit your ability to follow industry-established application guidelines.

Flash point

Asphalt's flash-point temperature is the lowest temperature at which asphalt vapors above a volatile combustible substance can ignite in air when exposed to an ignition source. Flash point is measured in a laboratory using ASTM D92, "Standard Test Method for Flash and Fire Points by Cleveland Open Cup Tester," and is unique to the asphalt supplier, production lot and type.

The U.S. product standard for roofing asphalt, ASTM D312, "Standard Specification for Asphalt Used in Roofing," establishes a minimum flash point of 500 F and indicates the actual flash point must be plainly marked on each container or bill of lading for bulk shipments. Actual flash-point temperatures well in excess of 500 F are common and desirable.