Silicone Spandrel Glass Opacifiers

Mitigating Glass Breakage Risk From Thermal and Other Stresses



Curtain wall design commonly uses insulating glass units for vision and spandrel glazing to provide better visual harmonization of building facade glass. Risks with this design approach include higher thermal stresses, especially when low-emissivity coatings are used on insulating glass units in spandrel areas. Ceramic enamel frit – commonly used to opacify spandrel glass – is known to induce a bending strength reduction of up to 50 percent. The ability of ceramic enamel frit coated glass to resist thermal stress is similarly reduced. Multiple incidences of thermal stress related fracture have occurred with heat-strengthened, ceramic enamel frit opacified spandrel glass. An increased chance of spontaneous breakage, by nickel sulfide inclusions, may occur if ceramic enamel frit opacified spandrel glass is fully-tempered to withstand the thermal stresses that it is exposed to.

Silicone spandrel glass coatings have been examined as a solution to prevent the strength reduction in heat-treated glass when ceramic enamel frit is applied as an opacifier. Four-point bending tests were used to investigate the flexural strength of coated heat-strengthened and fully-tempered glass. Ball drop testing was used to investigate the impact resistance of coated fully-tempered glass. Silicone coatings have no adverse effect on the flexural strength or impact resistance of the substrate and, in some instances, improve it. Therefore, silicone opacifiers do not reduce the resistance to thermal stress of heat-treated glass. These coatings also provide fallout protection in accordance with ASTM C1048 (ASTM, 2012). This suggests using a silicone opacifier on heat-treated spandrel glass could greatly reduce the risk of fracture resulting from thermally induced tensile stress, flexural stress, and impact related glass breakage in addition to reducing risk of injury from fallout if breakage occurs.


Photo of Scott Norville

Scott Norville

Professor, Department of Civil, Environmental, and Construction Engineering

Texas Tech University

Photo of Samir Blanchet

Samir Blanchet

Texas Tech University

Photo of George Torok

George Torok

Building Science Specialist

Morrison Hershfield

Photo of Kris Vockler

Kris Vockler


ICD High Performance Coatings

Photo of John Swanson

John Swanson

ICD High Performance Coatings

Photo of Chris Barry

Chris Barry

Photo of Lawrence Carbary

Lawrence Carbary


Photo of Stephane Hoffman

Stephane Hoffman

Vice President Facade Engineering

Morrison Hershfield

Photo of Timothy Krytenberg

Timothy Krytenberg

ICD High Performance Coatings

Photo of Chris Fronsoe

Chris Fronsoe

ICD High Performance Coatings


Introduction & Background

In the world of façade glass, there are two types of glass: vision, and spandrel. Vision glass is transparent to provide viewing areas for occupants and daylight for the interior

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Experimental Method

Study and procedure details about the two different experiment methods are defined below – what tools, software or models were implemented, how results were measured, etc.

Four-Point Bending Test

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Data & Explanation

Four-Point Bending Test

All specimen fracture origins lay between the load points on the beam specimens, that is, within the area of constant bending moment and flexural stress. No fracture

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Conclusion and Future Work

Four-point bending test results indicate OPACI-COAT® coatings have a positive impact on the flexural strength of HS glass, and have little to no impact on the strength of FT glass

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Rights and Permissions

ASTM “Standard Specification for Heat Strengthened and Fully Tempered Flat Glass.” ASTM C 1048-12e1, West Conshohocken, PA, (2012).

ASTM “Standard Test Method for Flexural Strengths of Advanced Ceramics at Ambient Temperature.” ASTM C 1161-13, West Conshohocken, PA, (2013).

ASTM “Standard Practice for Determining the Load Resistance of Glass in Buildings.” ASTM E 1300-16, West Conshohocken, PA, (2016).

Barry, Chris, Norville, H. Scott, “Unexpected Breakage in Ceramic Enameled (Frit) HS IG Spandrels.”

IGMA Winter Conference, FL, (Feb 5, 2015).

Beason, William L., “A Failure Prediction Model for Window Glass.” Institute for Disaster Research, Texas Tech University, Lubbock, (NTIS Accession No. PB81-148421), (May, 1980).

Bergers, Matt, Natividad, Kayla, Morse, Stephen M., Norville, H. Scott, “Full Scale Tests of Heat Strengthened Glass with Ceramic Frit.” Glass Structures & Engineering; Springer: Switzerland, Vol. 1, Issue 1, (2016): p. 261.

EN 1863-2 “Glass in Building – Heat Strengthened Soda Lime Silicate Glass – Part 2: Evaluation of Conformity/Product Standard.” BSI, Brussels, (2004).

EN 12150-1 “Glass in Building – Thermally Toughened Soda Lime Silicate Safety Glass.” BSI, Brussels, (2015).

GANA 76-12-10a “Fully Tempered Glass Uses Requiring Strength and Resistance to Temperature – Rev #1.” Topeka, KS, (2008).

Krampe, Philipp. “The Strength of Enamelled Glass.” In Challenging Glass 4 & COST Action TU0905 Final Conference; Louter, C., Ed.; Taylor & Francis: London, (2014): p. 691.

Maniatis, Iris, and Elstner, Michael. “Investigation on the Mechanical Strength of Enamelled Glass.” Glass Structures & Engineering; Springer: Switzerland, Vol. 1, Issue 1, (2016): p. 277.

Mognato, Ennio, and Barbieri, Alessandra. “The Breakage of Glass – Thermal Shock and Nickel Sulfide Inclusion.” COST Action TU0905, Mid-term Conference on Structural Glass; Mocibob, D. Louter, C., Ed.; CRC Press: Boca Raton, (2013): p. 155.

Natividad, Kayla, Morse, Stephen M., and Norville, H. Scott. “Tests of Heat Treated Glass with Full Coverage Ceramic Frit.” J. of Architectural Engineering, ASCE, (In Press).

NSG Group “Properties of Soda-lime Silica Float Glass.” NSG Technical Bulletin #129:, (January 2013): p. 1.