EXPERT ADVICE
in turn, has a flocculating effect on the
clay in the sealcoating formulation. In
simpler words, the clay particles flock
together when their respective electrical
changes (negative) are robbed by the posi-
tive charges, arising from the ionization of
the salts. And that is seen as thickening.
Although such materials are relatively
inexpensive and quite efficient as thick-
ener, they introduce permanent water
sensitivity in cured sealcoating films. In
other words, salt additives stay in the seal-
coatings film and re-absorb water at rain
events or under high ambient humidity.
The water thus re-absorbed swells the
sealcoating film which, in turn, is torn by
vehicular or pedestrian traffic. The pre-
mature failure of sealcoatings have been
attributed to poor water resistance in nu-
able consistency, as the homeowner is not
expected to be equipped with all kinds of
stirring gadgets.
Gums do a fair job in imparting the
right viscosity, through the formation of
gels within the sealcoating. They do not
affect the dispersion of clay and fillers in
the sealcoating, therefore, have lesser or
no tendency to destabilize the sealcoating
system.
Water sensitivity of gums is again the
major problem because they stay in the
cured film of sealer and re-absorb water
when it rains, or the humidity becomes
too high. The clays in the sealer, again,
swell as a result of water re-absorption,
rendering the sealcoating weak and vul-
nerable to traffic. Severe tracking prob-
lems have been reported in coatings using
nitic clays impart real thixotropy to seal-
coating formulations and their use is quite
frequent. Despite of their water sensitivi-
ty, bentonitic clays are essential for good
rheological control. The water sensitivity
of the sealcoating can be minimized with
judicious choice of ball clays and specialty
chemicals in the sealcoating formulations.
The cost effectiveness is good.
4. POLYMERIC THICKENERS
In the last few decades the industry has
witnessed the use of a myriad of latex ad-
ditives which have been claimed to deliver
all that a sealcoater could ever dream of;
some are true and some false. We will con-
fine our discussion to their use as rheolog-
ical additives. The latex chosen as rheolog-
ical additive must not have a destabilizing
rhe·ol·o·gy (/rē'älejē/)
the branch of physics that deals with the deformation and flow of matter, especially
the non-Newtonian flow of liquids and the plastic flow of solids.
merous situations.
The absorbed water is also capable to
re-emulsify the cured film under the
grinding action of the traffic. This is com-
monly seen as “brown colored” water
puddles. The process of “re-emulsifica-
tion” is the primary cause of the tracking
problem where the re-emulsified sealer is
likely to tracked into businesses or homes.
The use of these chemicals should, there-
fore, be avoided.
2. NATURAL GUMS
Xanthan Gum is used quite frequent-
ly, particularly for making pails products
for the retail markets. The retail products
are pre-blended version of sealcoating
materials where water and aggregates are
added at the time of manufacturing and
the final product is packaged in 5-gallon
pails. Since the product are designed as
ready-to-use, the major requirement is
no or very soft settling of the contents in
the pail. Furthermore, the contents in the
pails should be easy to re-disperse to us-
www.callape.com
natural gums as rheological additives.
Cost effectiveness is also poor.
3. BENTONITE CLAYS
These specialty clays have been com-
monly used since the inception of seal-
coatings formulations rheology control.
Bentonite is generally used in conjunc-
tion with ball clays in sealer formulations.
Bentonitic clays act as primary dispersants
for tar or asphalt in the water phase along
with the ball clays. They have the excep-
tional ability to form a firm (but false)
body in the sealcoating material which
breaks down easily under the pressure of
the brush, squeegee or spray, rendering a
good flow and leveling that are essential
for even coverage. The sealcoating mate-
rial stops flowing soon after the removals
of the pressure from the application tool.
This phenomenon in coatings flow behav-
ior is called ‘Thixotropy’; where the vis-
cosity drops on shearing action of brush,
squeegee or spray and reconstitutes when
the shearing actions is removed. Bento-
[26]
effect on the sealcoating material. The
sealcoatings frequently are formulated
with specialty chemicals, emulsifiers and
surfactants. The latex used should never
rob the electrical charges from the clay or
the bitumen particles, nor clash with the
specialty chemicals in the formulation.
Some latex additives have been found to
weaken the sealcoating film or make them
less resistant to chemicals. On the other
hand, some select polymeric rheological
additives boost the performance in real
terms like faster drying, uniform dried
color of the sealer, enhanced resistance to
petrochemicals, de-icing salts and overall
longevity.
The choice for the proper polymeric
rheology addictive is the key to superior
performance. The formulator or the seal-
coating professional is advised to familiar-
ize himself/herself with all the available
additives and their specific attributes, pri-
or to making the selection. The cost effec-
tiveness can be excellent with the choice
of the right material.
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