In a newly published paper by some big glass industry names, spandrel glass applications are shown to have reduced risk of thermal breakage and fallout if silicone opacifiers are used.
Curtain wall design commonly uses insulating glass units for spandrel glazing to provide better visual harmony between vision and spandrel areas. Risks with this approach include higher thermal stresses, especially when low-emissivity coatings are used, and increased chance of spontaneous breakage by nickel sulfide inclusions if fully tempered glass is used to control thermal stress. The thermal stress control benefit of heat treated glass is reduced if a ceramic enamel frit opacifier -which induces a known strength reduction of up to 40%- is applied. Incidences of thermal stress related fracture have occurred with heat strengthened, ceramic enamel frit opacified spandrel glass.
Silicone coatings have been examined as a solution to prevent strength reduction in heat-treated glass when applied as a spandrel 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. 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 and reduce the risk of injury from fallout if breakage occurs.