3.7.1.2
Mixing Topcoat Material
Do not mix partial kits, or alter mix ratios. Mix polyurethane coating
materials in same temperature conditions specified in article entitled
"Delivery and Storage." The polyurethane coating material is moisture
sensitive and any introduction of moisture or water into the material
during mixing or application will shorten usable pot life. Use a mixer
that does not create a vortex. Do not add solvent without specific written
recommendation from the manufacturer. No induction time is required, only
thorough agitation of the mixed material.
3.7.1.3
Pot Life
Apply mixed products within stated pot life for each product. Stop
applying when material becomes difficult to apply in a smooth, uniform wet
film. Add all required solvent at time of mixing. Do not add solvent to
extend pot life. Pot life is based on standard conditions at 21 degrees C
70 degrees F and 50 percent relative humidity. For every 10 degrees C 18
degrees F rise in temperature, pot life is reduced by approximately half,
and for every 10 degrees C 18 degrees F drop it is approximately doubled.
Usable pot life depends on the temperature of the material at the time of
mixing and the sustained temperature at the time of application. Other
factors such as the shape of the container and volume of mixed material may
also affect pot life. Precooling or exterior icing of components for at
least 24 hours to a minimum of 10 degrees C 50 degrees F in hot climates
will extend pot life. High humidity at time of mixing and application
shortens pot life of the Polyurethane topcoat material. Following are
approximate pot life times:
Sealant
As specified by manufacturer
Epoxy primer and intermediate materials
4 hours
Polyurethane topcoat materials
2 hours.
3.7.1.4
Application Conditions and Recoat Windows
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NOTE: These new requirements are provided in an
attempt to prevent the significant number of
intercoat delamination failures that are frequently
found on industrial structures. The very strict
requirements on application conditions and recoat
windows may require work during abnormal hours,
including weekends. Contractor work hours should
allow for such during coating application.
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NOTE: Cold-weather application is not covered by
this specification. If a project is designed for
coating in cold weather, then the enclosure and
heating requirements may be significant. It is not
intended that contractors be forced to apply
coatings in cold weather, however, the underlying
premise is that coatings must be applied within the
specified temperature ranges. A cold-weather
specification should not be used to simply save
money, as the coating system will generally not have
the same longevity as one applied within 60-100
degrees F.
SECTION 09971
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