Building Design and Construction Handbook - Merritt - Ventech!

4.100 SECTION FOUR
other because of changes in moisture content or temperature, (4) good durability
or the ability to maintain their properties over a long-period of time without marked
deterioration, and (5) no staining of surrounding materials such as stone.
4.86 CALKING COMPOUNDS
These sealers are used mostly with traditional materials such as masonry, with
relatively small windows, and at other points where motion of building components
is relatively small. They are typically composed of elastomeric polymers or bodied
linseed or soy oil, or both, combined with calcium carbonate (ground marble or
limestone), tinting pigments, a gelling agent, drier, and mineral spirits (thinners).
Two types of commonly employed, gun grade and knife grade. Gun grades are
viscous semiliquids suitable for application by hand or air-operated calking guns.
Knife grades are stiffer and are applied by knife, spatula, or mason’s pointing tools.
Because calking compounds are based on drying oils that eventually harden in
contact with the air, the best joints are generally thick and deep, with a relatively
small portion exposed to the air. The exposed surface is expected to form a tough
protective skin for the soft mass underneath, which in turn provides the cohesiveness,
adhesiveness, and elasticity required. Thin shallow beads cannot be expected
to have the durability of thick joints with small exposed surface areas.
4.87 SEALANTS
For joints and other points where large movements of building components are
expected, elastomeric materials may be used as sealants. Whereas traditional calking
compounds should not be used where movements of more than 5% of joint
width or at most 10% are expected, larger movements, typically 10 to 25%, can be
accommodated by the rubbery sealants.
Some elastomeric sealants consist of two components, mixed just before application.
Polymerization occurs, leading to conversion of the viscous material to a
rubbery consistency. The working time or pot life before this occurs varies, depending
upon formulation and temperature, from a fraction of an hour to several
hours or a day. Other formulations are single-component and require no mixing.
They harden upon exposure to moisture in the air.
Various curing agents, accelerators, plasticizers, fillers, thickeners, and other
agents may be added, depending on the basic material and the end-use requirements.
Among the polymeric materials employed are:
Acrylics: solvent-release type, water-release type, latex
Butyls: skinning and nonskinning
Polysulfide: two-part and one-part
Silicone: one-part
Polyurethane: two-part and one-part
Chlorosulfonated polyethylene: one-part
Polyurethane-polyepoxide: two-part