portion increases to nearly 70%, by volume.
Sealcoatings, like other water-based
coatings, dry and cure by releasing water
to the atmosphere. The optimum cure
and the full strength of the sealcoatings are
reached after the release of all the water. It
will be beneficial to understand how the
water is released from the sealer film and
the influencing pavement and ambient
conditions. It is imperative that sealcoating
professionals fully understand and appreciate
the importance of the factors that
influence the optimum cure, thus performance
of sealcoatings. Deviations may
result in poor performance and premature
failure of even the very best of the coatings,
if not applied and cured properly.
For optimum performance, sealcoatings
shall be;
• Mixed accurately according to the mix
design as agreed for the project i.e. the
proper dilution with water, sand loading,
additive content, etc.
• Applied at the proper coverage rate,
(expressed either in gallons/sq. yard or
sq.ft./gallon), on a properly cleaned and
repaired surface.
• Allowed to cure “thoroughly” under
a set of pavement and ambient weather
conditions which will allow the coating to
attain its optimal firmness. These “ideal”
conditions are simply the ambient and
pavement conditions that are specified by
the manufacturers and accepted by the industry
under which the sealcoatings shall
be applied and allowed to cure.
Sealcoating Basics
Sealcoating, based on either asphalt or
refined tar, is a stable dispersion of various
ingredients, in water. The major ingredients
are described below:
• Binder. The refined tar (RT-12) or
asphalt cement (AC) is called the binder
in sealcoatings. As you may know, both
asphalt and refined tar are thermoplastic
materials, meaning that they soften and
melt at higher temperatures and become
hard at cooler temperatures (below 60°).
The binder is the backbone of sealcoatings.
It is the ingredient that protects the
asphalt pavement. In the wet state (uncured),
sealer contains a fine dispersion of
binder particles in the range of 2 to 5 microns
(human hair is approx. 25 microns
or 1 mil), in either spherical or elongated
cigar shapes. Upon full cure the binder
forms the continuous film, tightly holding
all the fillers and sand/aggregate.
• Clay, fillers and aggregates are used to
impart proper toughness to the sealcoating
film and counteract the tackiness of
the binder at elevated surface temperatures.
• Specialty chemicals, such as surfactants
and emulsifiers are used to stabilize the
sealcoating systems.
• Water is the dispersing medium and the
carrier for all the components. In most
sealcoatings, water constitutes the major
component, approx. 60% by volume.
The Mechanism of Film Formation
Sealcoatings, like most water-borne
coatings, start releasing water into the ambient
atmosphere, as soon as applied. The
surrounding air acts as a blotting paper
to soak up the released water; its capacity
depending upon the relative humidity
(% R.H.) of the atmosphere. It will be explained
later. Sealcoatings attain full cure
through the loss of all the water from the
wet film. As the water leaves, the volume
of the wet film shrinks, in direct proportion
to its water content(by volume), in
the mix. For example, if the mix design
has 70% water by volume, the wet film
will shrink by 70%, i.e. 30% of its original
volume.
The evaporation of water from the wet
film produces a steady turbulence in the
film and forces the suspended particles
into a closer proximity). The film becomes
progressively denser, thus forcing the
binder particles to touch each other and
fuse into a continuous film, encapsulating
the filler particles in the process. Simultaneously,
the excess binder in the matrix
allows the film to effectively bond to the
pavement surface.
Descriptions such as the full cure, final
set or optimum strength mean that the
sealcoating has reached its full strength
and is capable of performing its task, as a
protective coating. A properly cured sealcoatings
forms a continuous film, free of
voids or imperfections, which stop water,
1.800.210.5923 [11]
August 2020