Spandrel glass is glass that has been rendered
near opaque, i.e., it is non-vision glass. Its major use is to mask
materials or construction from view from the exterior of a building.
Such areas are commonly the hung-ceiling area above a vision lite or
the knee-wall area below a vision lite. It is sometimes used to hide
a column in what is normally the vision-glass area.
The indoor surface of spandrel
glass is not suitable for use as a finished wall. Additional
suitable material, such as sheet rock, must be installed on the
indoor side when used in quasi-vision areas such as transom lites,
column covers, etc.
In order to reduce the probability
of glass breakage due to thermal stresses, spandrel glass should be
Methods of Fabricating
The most commonly used methods of rendering spandrel areas opaque
Ceramic Frit Opacification
Ceramic frit opacification consists of a coating of durable,
colored ceramic material that is compatible with the base glass and
is fire-fused into one surface of the glass during the heat-treating
process. Since the basic purpose is generally to render the glass
opaque, the ceramic frit is typically applied to the #2 surface of
monolithic glass or the #4 surface of an insulating unit. The
opacity can be improved with thicker or multiple coats of ceramic
If the application requires the
unit to be visible from both the exterior (#1) and interior (#4)
surfaces, ceramic frit with thicker and/or multiple coats can be
applied in order to provide an architectural finish when viewed from
the inside of the building. Note: In this case, the exterior lite
must have a very low level of light transmittance because of
inherent characteristics (pinholes, uneven appearance of the coating
etc.) in the ceramic frit layer. The manufacturer/fabricator should
be consulted for guidance in these applications.
Ceramic frit coatings are
available in a wide range of colors. The coating can be applied to
otherwise uncoated glass or, in most cases, to the interior surface
of a pyrolytically coated solar-control reflective glass, regardless
of which surface has the pyrolytic coating. Light color ceramic frit
applications may require a double coat in order to achieve a more
Glass with a fired-on ceramic frit
should not be used except with an opaque backup construction. If it
is used where light may be seen through the glass, consultation with
the glass fabricator is mandatory. Pinholes and uneven appearance of
the ceramic coating may be visible prior to the completion of the
opaque backup construction. These conditions are inherent in the
product and are not reason for rejection.
Film opacification consists of a factory applied polyester film
adhered to the coated surface of vacuum deposition or pyrolytic
coated glass by means of a solvent based adhesive. The polyester
opacifier was designed to be adhered to a metal surface and
therefore, should not be applied to the float glass surface of
uncoated monolithic glass or the uncoated inboard lite of an
insulating unit. Film opacified glass fabricators typically
recommend against adhering insulation or other materials to the
opacifier surface. The fabricator should be consulted for guidelines
concerning contact of other spandrel materials with the polyester
surface and airspace requirements behind the polyester surface.
A lite of glass with complete
coverage of polyester film opacifier can be fabricated to meet the
optional fallout resistance test contained in ASTM C 1048
Standard Specification for Heat-Treated Flat Glass - Kind HS, Kind
FT Coated and Uncoated Glass.
For structural silicone glazing
applications, the polyester film opacifier must be cut back to allow
for structural bonding to the coated glass surface. Glass in this
application will not meet the optional fallout resistance test
contained in ASTM C 1048.
Silicone opacification consists of an elastomeric film of liquid
silicone rubber applied to any glass substrate via; spray, roller
coater, or curtain coater. The chemistry utilizes strong bonding to
the similarly composed glass substrate for adhesion and durability.
Silicone opacifiers are applied after the heat-treating process and
may employ a large variety of color and specialty pigments.
The basic purpose of the product
is to render the glass opaque, thus can be applied to both
monolithic and insulating glass units. For monolithic applications,
the silicone opacification is applied to the #2 surface, and for
insulating glass units, to the #2, #3, or #4 surface, depending on
application. Edge deletion is required for all structural
applications, as well as the interior surface of an application of
an insulating glass unit. Compatibility confirmation should be
obtained from the spandrel manufacturer prior to installation.
Standard application thickness for
opacity is 8 mils wet or 3.5 mils dry. Opacity can be improved with
thicker or multiple coats of the silicone opacifier. To attain
fallout certification, the silicone opacifier must be applied at a
thickness of at least 13 mils wet or 5 mils dry. Silicone spandrels
will meet this classification if proper testing is documented per
GANA Tempering Division Specification No. 89-1-6 – Environmental
Durability of Fully Tempered or Heat-Strengthened Spandrel Glass
with Applied Opacifiers, ASTM C 1048, and CAN/CGSB-12.9-M91 –
A wide variety of silicone color
coatings can be applied to all glass substrates, including
especially pyrolytic and sputter coated reflective glass substrates,
without harming the reflective coating. As with all spandrel
products, silicone spandrels should not be used except with an
opaque backup construction. If it is used where light may be seen
through the glass, consultation with the glass fabricator is
Water-based silicone opacification
can be used and certified as “green” for the use in “green” building
applications, due to polymer chemistry and pigment usage.
Silicone opacification product
performance may vary between manufacturers. Consult with the
manufacturer/fabricator to confirm compliance with specification
Shadow Box Opacification
Shadow box opacification is achieved by enclosing the space
bounded by the vertical and horizontal mullions behind the glass.
This is accomplished by securing a painted metal pan or dark
matte-finished insulation board back from the glass. Typically, the
inner face of the pan or insulation is flush with the inner plane of
the vertical mullions. Shadow box detailing must also ensure that
surfaces of the glazing system and surrounding materials have a dark
surface to prevent read-through under some lighting conditions.
Note: The GANA Glazing Manual
(Section II - Fabricated Architectural Glass Products, pages 15-17)
should be consulted for additional detailed information on spandrel
glass design considerations, spandrel insulation and spandrel glass
inspection and glazing guidelines prior to specifying and using
spandrel glass constructions.
The above information is from the
GANA Glazing Manual, 2004 Edition - the most frequently
referenced resource in the architectural glass and glazing industry.
The Glazing Manual is an excellent addition to any technical
to order a copy of the manual or CD-ROM. For further information on
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