Structural silicone glazing (SSG)
Glass held to the frame by a structural sealant bond - flush and frameless, and wholly dependent on factory control.
Last updated 2026-09-05
What is Structural silicone glazing (SSG)?
Structural silicone glazing holds the glass onto the facade frame with a structural silicone sealant instead of with mechanical pressure plates and caps. The bond itself is the retention. Because there is no visible clamping across the face of the glass, the elevation reads as an almost continuous glazed plane with only a slim sealed joint between panes, and it is that flush, frameless appearance that architects specify SSG for. The system can be two-sided, with mechanical retention kept on two edges and structural bonding on the other two, or four-sided with every edge bonded, and the designer chooses which on the basis of the building and the risk.
It is essential to be clear about what the sealant is doing. In an SSG facade the structural silicone carries the weight or the wind load transfer of the glass, or both depending on the arrangement, and it does so permanently and in every weather over the life of the building. That makes the bond a life-safety element in exactly the same sense as a bracket or a bolt. It is designed by the facade engineer and the sealant manufacturer working together for that specific glass, that specific frame and that specific exposure, applied in a factory under controlled temperature, humidity and cleanliness by trained operatives, and released only after a documented cure and a quality regime run by the specialist. Nothing about that is negotiable and none of it belongs on a site scaffold.
The consequences shape the whole package. SSG is almost always a factory operation within a unitised system, because the surface preparation, the primer where one is required, the application conditions, the cure and the testing simply cannot be reproduced outdoors. Substrate compatibility, cleaning procedure, adhesion, cure control and traceability of every batch are all part of the specialist's quality system, and the records follow the units to site. On site the units are handled and installed like any other unitised unit, with damage to the bonded edge treated as a rejection rather than a repair. Maintenance and eventual replacement are planned into the facade strategy, and any later intervention to a bonded unit goes back to the specialist, not to a maintenance contractor with a sealant gun.
How does Structural silicone glazing (SSG) work, step by step?
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Step 1: Establish the concept and the risk position
The design team and the facade engineer decide whether SSG is appropriate at all, and if so whether the system is two-sided or four-sided, on the basis of the building height, the exposure, the consequence of a failure and the maintenance strategy. Two-sided systems keep mechanical retention on two edges and are less onerous in risk terms; four-sided systems give the fully flush appearance and rely wholly on the bond. On many projects secondary retention or a defined inspection and replacement regime is required, and that decision belongs with the designers at concept stage rather than with the fabricator later.
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Step 2: Design the bond with the sealant manufacturer
The structural sealant joint is engineered for the specific combination of glass, frame material and finish, exposure and movement, with the sealant manufacturer involved directly. The manufacturer confirms compatibility of every material that will touch or sit near the bond, sets out the surface preparation and any primer, and states the conditions under which the sealant may be applied and cured. No dimensions, mix or cure data are matters of general practice - they are project-specific outputs of that design, issued to the fabricator as a controlled procedure.
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Step 3: Qualify the fabricator and the process
The bonding is carried out only by a specialist with a controlled, audited process: a clean bonding area, controlled temperature and humidity, trained and named operatives, calibrated equipment and full traceability of sealant batches. Before production runs, the process is proven on samples and the specialist's quality plan is agreed with the facade engineer. On most projects the client's team or an independent inspector audits the facility, because it is not possible to verify a completed bond by looking at the finished unit on site.
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Step 4: Prepare the substrates and apply the sealant in the factory
Glass edges and frame surfaces are cleaned and prepared exactly to the manufacturer's procedure, primed where required, and bonded within the working time the procedure allows. Setting blocks, spacers and any backing are placed as detailed so the joint forms as designed. Application is continuous and voids are not acceptable, so the joints are worked and inspected as they are made. Every unit is identified so that the batch, the operative, the date and the conditions can be traced back if a question arises later.
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Step 5: Cure and release under a documented regime
The bonded units are held in controlled conditions until the sealant has cured, and they are not moved, glazed on, transported or loaded until the specialist releases them against the manufacturer's procedure. Adhesion is verified by the specialist's own testing regime on samples taken from production, with the criteria set by the sealant manufacturer and the facade engineer. A unit that fails is quarantined and the cause investigated across the batch, not repaired quietly. The release records travel with the units.
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Step 6: Transport and install without damaging the bond
Bonded units are transported in purpose-made frames and handled with vacuum lifters and manipulators, because the bond line is the last thing that should ever take a knock. On site the units are installed exactly as any other unitised unit - hung on brackets set from a survey, aligned, and the joints made up - with the perimeter weather sealing kept distinct from the structural bond so that the two are never confused. Any unit arriving with damage to the bonded edge or the glass edge is rejected and returned, because site repair of a structural bond is not an option.
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Step 7: Record, protect and plan the maintenance regime
Traceability records, release certificates and the as-installed unit schedule are handed over as part of the facade documentation, because they are the evidence that a life-safety bond was made correctly. The maintenance strategy sets out the inspection regime for the weather seals and the bonded joints, the access needed to reach them, and the procedure for replacing a damaged unit - which is a specialist operation using a like-for-like factory-bonded replacement. Any later alteration, cleaning agent or applied product near the bond is checked for compatibility with the specialist before it is used.
What are the benefits of Structural silicone glazing (SSG)?
- Flush, frameless external appearance with no visible pressure plates or caps across the glass
- Slim sighted joint lines maximise the glazed area and give the clean elevation architects specify
- Factory bonding gives controlled, consistent quality that no site operation can match
- No external capping to collect dirt or to be removed at height for maintenance
- Works naturally within unitised systems, so the facade keeps the speed of unitised installation
- Sealed joint accommodates movement well when designed for the specific building
What are the limitations of Structural silicone glazing (SSG)?
- The bond is a life-safety element, so the whole system depends on the specialist's process control
- Cannot be carried out on site - factory conditions, cure control and traceability are non-negotiable
- Compatibility of every adjacent material has to be confirmed by the sealant manufacturer
- Damage to a bonded edge means rejection and replacement, not repair
- Higher cost, longer lead time and a heavier documentation and audit burden than capped systems
- Later alterations, replacement units and even cleaning products need specialist involvement
What is Structural silicone glazing (SSG) best suited for?
What plant does Structural silicone glazing (SSG) need?
- Controlled factory bonding area with temperature, humidity and cleanliness monitoring
- Calibrated sealant dispensing and mixing equipment with batch traceability
- Surface preparation and cleaning equipment to the manufacturer's procedure
- Sample preparation and adhesion testing facilities within the specialist's quality system
- Purpose-made transport frames, vacuum lifters and glass manipulators
- Standard unitised installation plant on site - hoists, monorails or cranes, and internal access
How is Structural silicone glazing (SSG) quality-checked?
- Fabricator qualified and the bonding process audited before production release
- Material compatibility confirmed in writing by the sealant manufacturer for every adjacent material
- Surface preparation, priming and application conditions recorded for each production run
- Sealant batch, operative, date and conditions traceable for every bonded unit
- Adhesion testing on production samples to the criteria set by the manufacturer and the facade engineer, with failures quarantined and investigated across the batch
- Release certificates and the as-installed schedule handed over, with a defined inspection and replacement regime