c. Plastisol (PVC); a two-coat system consisting of
a polyvinyl-chloride resin dispersed in a
plasticizer top-coat over a corrosion-resistant
primer; it is a high-performance, thick coating
designed for highly aggressive and corrosive
environments with excellent resistance to common
acids, alkalis, and inorganic compounds.
Most coatings may be ordered extra-thick for
buildings in direct contact with salt or chemical
laden air or where a premium finish would be
justified. The thicker coating provides additional
primer and increases the coating's corrosion and
abrasion resistance but it requires a special run by
the coil coater, at least a 22 degrees C (70 degrees
F) environment, and additional delivery time.
Appropriate specification requirements must be added
if the thick film coatings are to be used.
The high cost of preventing corrosion of galvanized
steel panels, together with the fact that cut edges,
scratches and penetrations of the panels expose the
steel substrate, warrants consideration for the use
of solid aluminum which is inherently less
susceptible to damaging corrosion.
Exterior wall and roof panels are available in
several standard colors. Standard trim colors are
usually more limited. Except where interior
surfaces receive a factory color coat, the exposed
reverse side of the panels normally are provided
with an off-white backer coating. Color other than
manufacturer's standard colors will be used only
when the extra cost is justified.
The choice of coating for the interior face of
panels depends on environmental and aesthetic
considerations. Where a corrosive atmosphere is
anticipated within the structure, the finish should
be PVF2 in a thickness appropriate to the
environment. For utilitarian facilities with little
likelihood of a detrimental atmosphere, a standard
backer coat is appropriate. Backer coat is the
manufacturer's standard coating (usually polyester
based) applied to the back side of the metal panel.
This coating is normally a wash coating and is not
controlled for consistent color or gloss. Where
interior surfaces are concealed behind insulation,
liner panels, etc.; provide only a primer coat.
These finishes should not be confused with a wash
coat which is used primarily to facilitate the coil
forming process and which is not closely controlled
for color, gloss or film thickness. The designer's
rationale for using any special interior finish
should be reflected in the design analysis.
Energy considerations must be included in the choice
of standard colors for the roof panels. White or
light-colored roofing surfaces are much better at
SECTION 13120
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