Spandrel Glass
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 heat-strengthened.
Methods of Fabricating Spandrel Glass
The most commonly used methods of rendering spandrel areas opaque are: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 frit.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 uniform appearance.
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
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
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 – Spandrel Glass.
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 mandatory.
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 performance requirements.
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 library. Go here to order a copy of the manual or CD-ROM. For further information on this and other GANA reference documents visit the PUBLICATIONS section of the GANA website.
