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ISO 28278-2: Assembly Rules for Structural Sealant Glazing
Quality-controlled assembly and bonding guidelines for SSG systems in building construction
Introduction to ISO 28278-2 Assembly Rules for SSG
ISO 28278-2:2010 provides comprehensive guidelines for the assembly and bonding of glass elements in structural sealant glazing (SSG) systems. This standard addresses the critical gap between design intent and field execution, ensuring that SSG assemblies are fabricated under controlled conditions with rigorous quality control protocols.
ISO 28278-2 makes a clear distinction between the designer (responsible for structural calculations) and the assembler (responsible for workmanship). The assembler is not responsible for design but must have access to design guidance (Annex C) to understand the information required from the designer.
The standard applies to SSG systems for use in facades and roofs with specific slope requirements: vertical facades are those with an inclination less than 15 degrees from vertical, and glass with a slope exceeding 50 degrees from vertical is considered unsupported. Only metallic substrates, uncoated glass, coated glass, and ceramic frit enamelled glass are within scope.
| Clause | Topic | Key Requirements |
|---|---|---|
| 4 | Environmental conditions | Temperature 15-30 C, humidity <75%, protected from dust and rain |
| 5 | Assembly/bonding | Controlled workshop conditions, proper surface preparation |
| 6 | Assembly control | Quality assurance system, inspection and testing tables |
| Annex A | Dynamic peel test | Adhesion verification of structural sealant |
| Annex C | Design guidance | Calculation methods for sealant dimensions |
| Annex D | Adhesion tests | In-process adhesion quality control |
Engineering Design Insights for SSG Assembly Quality
The standard emphasizes that quality control of the assembly process is of the highest importance. Clause 6 establishes minimum requirements for acceptable quality control, including organization responsibilities, a quality assurance system, and detailed inspection and testing tables for each stage of assembly. The assembler must maintain documented records of all bond tests, environmental conditions, and sealant batch information.
Environmental conditions during bonding are strictly controlled: temperature must be between 15 C and 30 C, relative humidity below 75%, and the work area protected from dust, rain, and direct sunlight. These conditions are non-negotiable for achieving reliable structural bonds.
Key Testing Protocols
Annex A specifies the dynamic peel test for structural sealant adhesion verification. Annex B describes the dynamic tensile test (informative). Annex D provides adhesion tests specifically for assembly/bonding control, including the important “H-test” for determining sealant cure state and adhesion quality. The skin-over time/elastomeric test (Annex F) ensures that the sealant cures properly within the specified working time.
The compatibility with adjacent materials (Annex E) is particularly important for engineers. Different gaskets, setting blocks, and spacer materials can chemically interfere with silicone sealant curing. Each material combination must be tested for compatibility before production use.
Design Guidance for Assemblers
Annex C provides design guidance that helps assemblers understand the design considerations behind SSG systems. It covers calculation of structural sealant bite depth and width based on wind load, dead load, thermal movement, and seismic loads. The sealant design stress values are provided for different load combinations, distinguishing between the creep factor (shear design stress under permanent static load) and short-term wind load capacity.
Practical Implementation in the Workshop
The assembly rules in Clause 5 detail the bonding process from surface preparation through sealant application to initial cure. Surface preparation is critical — glass surfaces must be cleaned with appropriate solvents, and metal substrates must be properly prepared according to the sealant manufacturer’s instructions. The standard requires that sealant be applied in a continuous bead without voids or air pockets, and that the bond line thickness be controlled within specified tolerances.
Frequently Asked Questions
Q1: What environmental conditions are required for SSG assembly?
A: Temperature 15-30 C, relative humidity below 75%, and protection from dust, rain, and direct sunlight. These conditions must be maintained throughout the bonding and initial cure period.
A: Temperature 15-30 C, relative humidity below 75%, and protection from dust, rain, and direct sunlight. These conditions must be maintained throughout the bonding and initial cure period.
Q2: What is the difference between cohesive and adhesive failure?
A: Cohesive failure occurs within the sealant material itself, while adhesive failure occurs at the bonding surface (sealant-to-glass or sealant-to-frame). Structural SSG bonds should exhibit cohesive failure in testing, indicating proper surface preparation and adhesion.
A: Cohesive failure occurs within the sealant material itself, while adhesive failure occurs at the bonding surface (sealant-to-glass or sealant-to-frame). Structural SSG bonds should exhibit cohesive failure in testing, indicating proper surface preparation and adhesion.
Q3: How does the assembler verify sealant compatibility?
A: Through compatibility testing as described in Annex E, which evaluates the effect of adjacent materials (gaskets, spacers, setting blocks) on sealant adhesion and cure. Each material combination must be tested before production use.
A: Through compatibility testing as described in Annex E, which evaluates the effect of adjacent materials (gaskets, spacers, setting blocks) on sealant adhesion and cure. Each material combination must be tested before production use.
Q4: What slope ranges does ISO 28278-2 cover?
A: Vertical facades (<15 degrees from vertical), inclined glazing (15-50 degrees), and unsupported glazing (>50 degrees). Roof applications with different slope ranges are also addressed.
A: Vertical facades (<15 degrees from vertical), inclined glazing (15-50 degrees), and unsupported glazing (>50 degrees). Roof applications with different slope ranges are also addressed.
