Term Description
Equiviscous temperature (EVT)

The temperature at which a bitumen attains the proper viscosity for built-up membrane application.

Equiviscous temperature (EVT) application range

The recommended bitumen application temperature range. The range is approximately 25 F below the EVT to 25 F above the EVT (50 degree Fahrenheit span). The EVT is measured in the mop cart or mechanical spreader just prior to application of the bitumen to the substrate.

Equiviscous temperature (EVT) for asphalt

The recommended EVT for roofing asphalt (ASTM D312, Type I, II, III or IV) is as follows:
mop application: the temperature at which the asphalt’s apparent viscosity is 125 centipoise.

mechanical spreader application: The temperature at which the asphalt's apparent viscosity is 75 centipoise. Note: To avoid the use of two kettles if there are simultaneous mop and mechanical spreader applications, the EVT for mechanical spreader application can be used for both application techniques.

Equiviscous temperature (EVT) for coal tar

The recommended EVT for roofing coal tar (ASTM D450, Type I or III) is the temperature at which the coal tar’s apparent viscosity is 25 centipoise.