01 May 1999
EQUIVISCOUS TEMPERATURE (EVT)
NRCA Bulletin 2-91 (December 1991)
Supersedes Bulletin #2 dated September 1988
The National Roofing Contractors Association (NRCA) makes the following recommendations
regarding bitumen application temperatures for built-up roof systems.
Equiviscous Temperature (EVT): The temperature at which a bitumen attains the proper viscosity for
built-up membrane application.
EVT Range: The recommended bitumen application temperature range. The range is approximately
14oC (25oF) above or below the EVT, thus giving a range of approximately 28oC (50oF). The EVT
range temperature is measured in the mop cart or mechanical spreader just prior to the application of
bitumen to the substrate.
EVT for Asphalt: The recommended EVT for roofing asphalt (ASTM D312, Type I, II, III, or IV) is as
a. Mop Application: The temperature at which the asphalt's apparent viscosity1 is 0.125 Pas
Note: If there are simultaneous mop and mechanical spreader applications, in order to avoid
the use of two kettles, the EVT for mechanical spreader application may be used for both application
b. Mechanical Spreader Application: The temperature at which the asphalt's apparent viscosity*
is 0.075 Pas (75 centipoise).
EVT for Coal Tar: The recommended EVT for roofing coal tar (ASTM D450l,Type I or III) is the
temperature at which the coal tar's apparent viscosity1 is 0.025 Pas (25 centipoise).
Product Labeling: NRCA recommends the following information be marked on each bitumen carton
label or, for bulk material, provided on the bill of lading:
a. Product Type: Bitumen type and ASTM designation (e.g., Asphalt--ASTM D312, Type III; or
Coal Tar--ASTM D450, Type III).
b. EVT: For asphalt, the EVT for both mop application and mechanical spreader application
should be given.
Flash Point (as determined by ASTM D92).
Apparent viscosity is measured by ASTM D4402. Viscosity is a measure of the resistance to flow of a
liquid. Pascal Second and Centipoise are units of a liquid's apparent viscosity.