EXPERT ADVICE
er particles are immobilized and do not fuse,
properly. Devoid of the proper fusion process,
binder particles do not effectively envelop
the clay and filler particles in the sealer film
to attain the proper hardness. They stay as
thermoplastic entities in the film, which become
sticky and soft under hot ambient and
pavement temperature conditions, thus causing
potential “tracking” problems, where the
sealer is liable to be tracked on to the floors or
carpets, etc.
2. Relative Humidity (R.H.) or Humidity
The Relative Humidity (R.H.) plays a significant
role in the cure mechanism. It directly
influences the rate of water loss from the
sealcoating film. Relative humidity (R.H.) is
the ratio of the actual moisture content of the
air, at a specified temperature, to its total capacity.
For example, 50% R.H. means that
only half of the air’s total capacity to hold water
has been used and it is capable of absorbing
another 50% of moisture or vapor from
the surroundings.
Conversely, 90% means that the ambient
air is loaded with moisture and has very little
(only 10%) capacity left to hold additional
water. Sealcoating applied under highly
humid conditions take a long time to cure
because there is very little room for the ambient
air to absorb the released water from
the film. The sealer film will release only the
amount of water that can be accommodated
by the atmosphere. The atmosphere and the
surrounding environment can be thought of
as a sheet of paper towel: when dry it will
soak up the spill but will not mop up if the
towel is too wet. Sealcoatings, understandably,
will cure faster at lower humidity than
at higher humidity. Under highly humid
conditions, sealcoatings shall be allowed
longer drying time before the application of
the subsequent coats and finally opening to
traffic.
The interdependence of temperature and
relative humidity on the water evaporation
rate is more than 3 times faster at 40 % R.H.
than 80%, at a given temperature.
3. Wind Velocity
The drying and cure times specifications do
not take wind velocity or air movement under
consideration, however, it is a known
fact that air movement, especially under
highly humid conditions, helps sealer dry
faster than without any air movement. A
light breeze assists in the dissipation of the
water and volatiles from the immediate vicinity.
Conversely, under low humidity conditions
(below 20-25%). the air movement
may cause the sealcoat to dry a bit too fast.
SUMMARY
Sealcoatings being water based, cure by
releasing all the water from their applied
films. For their optimum performance, the
cure conditions must be right. The cure
of sealcoatings is decisively influenced by
ambient and surface temperature, relative
humidity and wind velocity. Sealcoatings
cured under improper conditions are liable
to have inferior performance characteristics.
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7132 N Scott Rd | Saint Johns, MI 48879
989-224-4581
EMAIL: [email protected]
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