Low-Range
Sealants
The sealants that fall into the low-range category
can easily be identified by their low cost. They
generally include the oil-based, resin-based, resinous
caulks, bituminous-based mastics, and polybutene-based
sealants. They are generally very highly filled
with inexpensive principally mineral, fillers.
Some low-range
sealants are now siliconized. This generally means
that they contain between 0.20% and 2% of a silicone
fluid for better and greater plasticity, or a silicone
(silane) coupling agent for better adhesion, or
a silicone (silica) filter for better thixatrophy
or some other handling characteristic. A siliconized
oleoresinous or other low-range sealant is close
in performance to the parent material with no silicone,
silane, or silica in it. The most noticeable difference
between the siliconized and standard products is
usually the very large size of the work "silicone"
on the label.
Low-range caulks
were the standard of the industry in the early part
of the century and still enjoy some popularity in
the over-the-counter market because of their low
cost. Commercially (industrially) low-range caulks
are generally not used except in easily accessible
locations with very mild environments where re-caulking
would require only minimal labour cost. The labour
of re-caulking and the frequency of re-caulking
needed with these materials, keep their usage in
commercial construction to a minimum. It is this
author's opinion that the low-grade caulks would
be losing market share even faster if it were not
for the exploitation of the work "siliconized"
on the label, which gives the consumer the impression
that the caulk is a low-cost silicone.
Medium-Range
Sealants
Medium-range sealants have generally been limited
to applications with movements from 0 to 5% of the
joint width. In the 1970's however, some materials
in this range were marketed with movement capabilities
up to ±12.5% of the joint width. Such is
the case in the mid 1980's as well. While the ability
to take more movement is an important feature, the
chief advantage of these materials over the low-range
caulks is their longer service life. Manufacturers
of these materials often advertise 10 year and 15
year lifetimes, if the environment is protected
and the movement is low or non-existent. Actual
effective lifetime in the range of 3 to 10 years
is typically experienced.
A disadvantage
common to most sealants in this category is shrinkage,
which can approach 30% in some products. Plasticizers
that discolour paints, walls, and windows have been
a problem in some highly plasticized butyls, as
well as in most plasticized systems. The nonskinning
butyls, which are acceptable for buttering some
splice joints, acoustical sealing, and other hidden
joints are not considered to be part of this group.
Sealants in this
class do include the better butyls and latex acrylics
(but not PVA [vinyl] latex products, which are generally
in the low range category). This category also includes
the neoprenes as well as the solvent-release acrylics.
The characteristics most noted by the consumer is
the price, generally between the low- and high-range
sealants. These sealants, with the exception of
the odorous solvent acrylics, are generally easy
to apply. As with the low-range sealants, many sealants
of these general types were reintroduced to the
market in the early 1980's as siliconized, or advertised
as containing an additive of silicone and sometimes
called modified silicones.
Extensive work
by this author has shown the siliconized materials
he studied to be very close in performance to the
parent sealant and very far from the typical silicone
sealants. Siliconizing medium-range sealants has
no more benefit, other than marketing, than it did
for the low-range caulks. Some specific properties,
such as adhesion, extrudability, or consistency,
were improved by the 1-2% of silicone or silane
added. But the key performance properties of cyclic
joint movement ability, tolerance to harsh weather
conditions, tolerance to high temperature, and longevity
showed little if any improvement. The best of the
modified silicones studied by this author were really
polyether chain-type sealants cured with a silane
cross-linking mechanism and were called "modified
silicone" and not "siliconized".
Many of the standard polyurethanes have a polyether
chain, and the performance of what are called modified
silicones closely approaches that of the polyurethanes
and will be discussed with the high-range sealants.
High-Range
Sealants
High range sealants include polysulfides, urethanes,
and silicones, and certain proprietary modifications
of these materials. These sealants have many important
attributes, but of primary importance is their ability
to take joint movement of greater than ±12.5%.
Sealants in the high-range group are advertised
for from ±25% movement to ±50% or
±100%/-50% movement. It is generally from
this class that commercial sealants are chosen.
Some effort will be spent here to describe the key
features of each of these high-range sealants. The
property checklist developed in the article "Checklist
for Sealant Selection" can be compared to the
performance values given here. Thus a better grasp
on the variety of sealants available to satisfy
a need should be achieved.
