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 opacifier is applied (with a strength reduction of up to 40%) causing a number of breakage incidences with heat-strengthened spandrels.
Silicone coatings have been examined as a solution to prevent strength reduction in all heat treated glass when applied as a spandrel opacifier. Ring-on-ring, 4-point bending and ball drop testing were used to investigate the flexural strength of coated annealed, heat-strengthened and fully tempered glass. Silicone coatings have no adverse effect on the flexural strength of the substrate and, in some instances, improve it. These coatings also provide fallout protection in accordance with ASTM C1048. This suggests using a silicone spandrel opacifier on heat treated glass could greatly reduce the risk of spandrel glass breakage and reduce risk of injury from fallout if.