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Built-Up Roofing Specifications |
3. The Equiviscous
Temperature (EVT). As currently defined by ASTM, this is the temperature at which the
asphalt viscosity is 125 centistokes. Asphalt applied within ±25°F (± 14°C) of the EVT
at the point of application, will provide a nominal 23-25 pounds of asphalt per 100 square
feet (1.12 - 1.22 kg/m2).
4. The Finished Blowing Temperature (FBT). This is the
temperature at which the blowing of the asphalt is completed.
6.7.6 Work done by NRCA has shown that
different EVT values should be used for mop-applied asphalt and machine-applied asphalt.
Mop-applied asphalt should be applied at an EVT based on 125 centipoise, while
machine-applied asphalt should be applied using an EVT based on 75 centipoise. ASTM is
currently evaluating incorporating this information into its specifications. Some asphalt
suppliers are now including both EVT values on their product. If only the 125 centipoise
(centistokes) value is provided, then for machine application, the asphalt should be
applied at a 25°F (14°C) higher temperature than the 125 centipoise values.
6.7.7 JM requires adherence to the
following guidelines when the above information is furnished:
1. Use the proper softening point asphalt as specified for
the roof slope and material.
2. For optimum application, the asphalt should be at the
Equiviscous Temperature, ±25°F (± 14°C), at the point of application.
3. Never heat the asphalt to or above the Flash Point (FP).
Heating in excess of the Flash Point can cause the asphalt to ignite, causing a fire.
4. Heating above the Finished Blowing Temperature (FBT)
should be strictly regulated, never for longer than 4 hours, to preclude excessive asphalt
degradation.
6.7.8 The characteristics per ASTM D 312
of the various grades of asphalt are as follows:
6.7.9 If Equiviscous Temperature is
not available, nominal heating temperature guidelines of the asphalt are as follows:
Recommended Temperatures
6.7.10 Use of
insulated buckets and insulated circulating lines for cold weather application can help
maintain a proper EVT when temperatures are low and the distance from the asphalt source
to the point of application is
great.
6.7.11 When asphalts are applied within
the EVT temperature
ranges, the
proper amount of asphalt will be placed between the plies. The recommended quantity of
asphalt has been indicated on each specification in the current Johns Manville
Commercial/Industrial Roofing Systems Manual. Regardless of the exact quantity of asphalt
applied, it is important that the asphalt be con-tinuous, so felt does not touch felt, and
that there be full adhesion between all plies of the system. JM considers a ±25%
deviation from the asphalt
quantity listed to be acceptable.
6.7.12 Asphalt can come from a variety of
crude sources. Many of
these
sources produce high quality mopping grade asphalts and many do not. Various physical
properties of asphalts can affect the performance of the roofing system. For this reason,
JM qualifies asphalt sources throughout the country and requires that only these asphalts
be used to assure good performance and compatibility with the roofing products being used.
JM requires the use of Trumbull or another JM "approved" asphalt within systems
which require a JM Roofing Systems Guarantee. These "approved" asphalts are
periodically tested to assure con-formance to both ASTM and JM asphalt specifications. The
JM Approved Roofing Contractor must indicate at the time they place their orders that the
asphalt required will be used within a JM roofing system. This will ensure that the
asphalt supplied is registered with the asphalt source. The asphalt supplier will provide
a "JM" number to the asphalt purchaser which the Contractor in turn provides to
JM as a condition of issuance of the JM Guarantee. For the names of approved asphalt
suppliers in your area, contact a
JM sales representative.
6.8 Modified Asphalt
6.8.1 PermaMop is a modified asphalt with
a softening point of
between
210-225°F (99-107°C). While the softening point is comparable to an ASTM D 312, Type IV
asphalt, its other physical properties are more comparable to a lower melt point standard
asphalt. As a result, PermaMop offers many of the adhesion and weathering advantages of a
low melt point asphalt without the slope restrictions of a softer standard asphalt.
