What makes a sealant structural
A standard sealant is designed to seal a joint against air, water and contaminants. It fills the gap, accommodates a degree of movement and prevents ingress. Structural sealant does all of that, but it also provides a load-bearing bond between the elements it connects.
In a structural glazing application, for example, the sealant is not just weatherproofing the joint – it is holding the glass unit in place. The sealant carries tensile and shear loads as the building moves, the glazing flexes and thermal expansion acts on the assembly. That load-carrying requirement drives the specification toward products engineered specifically for structural performance, typically silicone-based systems tested and approved to relevant standards.
Where standard sealant is appropriate
Standard or general-purpose sealants are suitable where the joint only needs to seal rather than bond or carry load. Internal movement joints, sanitary sealant around fixtures, acoustic joints and non-structural weather seals on facades where a separate mechanical fixing carries the load are all appropriate applications.
The risk comes when a standard product is applied in a location where structural performance is needed – either because the specification was unclear, the wrong product was substituted on site, or the application was not properly understood during installation. In those cases, the joint may appear fine initially but will not perform over time under the movement and load demands placed on it.
Curtain wall and structural glazing systems
Curtain wall and unitised glazing assemblies are among the most common applications where structural sealant is a primary component of the system. The sealant bonds glass units to aluminium framing or directly to the building structure, meaning the integrity of the bond is critical to both weather performance and the safety of the facade.
These applications typically require a specific approved product from the glazing system manufacturer, applied using a defined preparation and installation process. Deviation from that process – whether in product selection, joint dimensions, primer specification or application technique – can affect the approval of the system and the long-term performance of the installation.
Facade panel joints and cladding interfaces
On commercial facades with cladding panels, stone elements or composite systems, structural sealant is used where the joint between panels needs to accommodate movement while maintaining both weather exclusion and bonding continuity between elements. The distinction from a standard weather seal here is the movement accommodation requirement – facades move, and the sealant must flex without losing adhesion to either substrate over repeated cycles.
Joint design also matters in these applications. The width and depth of the joint, the backing material specified and the surface preparation of the substrates all affect whether the sealant can perform as intended. A correctly designed and installed joint on a facade can last the life of the building with minimal intervention. An incorrectly designed one will fail progressively regardless of the product used.
Product selection in practice
Where a structural sealant application is prescribed in a specification, the product and system will usually be defined. The role of the contractor is to apply it correctly – which means following the manufacturer’s preparation requirements, using compatible primers where specified and ensuring joint dimensions fall within the product’s performance envelope.
Where selection is part of the scope, the key inputs are substrate type, joint dimensions, the degree and type of movement the joint needs to accommodate, and the environmental exposure conditions. Structural silicone products dominate most facade and glazing applications, but the correct grade and formulation still need to be matched to the specific demands of the assembly.
Remedial work and sealant replacement
When structural sealant fails on an existing building, the question of whether to reseal or replace the wider system depends on what has failed. Where the failure is in the sealant itself – adhesion loss, cohesive cracking, hardening or shrinkage – remedial resealing with a compatible product is often the appropriate response. Where the substrate has degraded, the joint geometry has changed or the wider assembly has been compromised, a more involved assessment is needed before resealing is confirmed as the right scope.
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