Sealants, Thermal Break Profiles & Curtain Wall Joint Performance
How joint design, structural silicone, EPDM gaskets and polyamide thermal breaks determine a curtain wall's air-tightness, water-tightness and U-value. The performance of a modern curtain wall depends as much on the materials hidden within its joints as on the glass and aluminum that dominate its visible surface. This article examines the engineering behind sealant selection, gasket specification, thermal break design and the failure modes that threaten facade durability across decades of service.
- Hanart Engineering Blog
- 8 October 2026
- 5 field photographs
Photographs from the Programme
Real Hanart site and factory photography — the discipline described below, seen in the field.
The Engineering View
Joint Types in Curtain Wall Systems
Curtain wall joints serve four distinct functions: structural bonding, weather sealing, thermal separation and movement accommodation.
Structural silicone joints. In four-sided SSG systems, the silicone adhesive carries glass dead weight and resists wind loads. The joint is designed with a width-to-depth ratio between 2:1 and 3:1, typically 12 mm wide by 6 mm deep. Structural silicone must achieve minimum tensile strength of 0.5 MPa and elongation at break above 150 percent per ASTM C1184. Substrates must be primed with manufacturer-approved primer to ensure adhesion to anodized aluminum and ceramic-fritted glass.
Structural Silicone Glazing (SSG) Adhesives
Structural silicone is the most critical adhesive in modern curtain walls. A failure risks glass fallout, air infiltration and water penetration.
Neutral-cure versus acetoxy-cure. Neutral-cure silicones release alcohol during curing and are compatible with metals, coated glass and stone substrates. Acetoxy-cure silicones release acetic acid that corrodes anodized aluminum. Hanart exclusively specifies neutral-cure structural silicones, typically two-part for factory assembly and one-part for field repairs.
Weatherseal Sealants & Movement Capability
Weatherseal sealants protect curtain wall joints from air and water infiltration while accommodating the movement that structural silicone cannot absorb. The selection of weatherseal sealant is governed by joint width, expected movement, environmental exposure and aesthetic requirements.
Movement capability: Class 25 versus Class 50. Class 25 sealants accommodate plus or minus 25 percent of the joint width. Class 50 sealants accommodate plus or minus 50 percent. Hanart specifies Class 25 for most panel-to-panel joints in unitized systems, where thermal movement is moderate. Class 50 is used for expansion joints, structural movement joints and interfaces with dissimilar materials such as concrete or steel, where differential movement is large.
Stage by Stage
Talk to a Sealant Specialist
Discuss your project's sealant specification, thermal break requirements and joint detailing with a Hanart facade engineer. We provide material selection guidance, compatibility testing and application supervision for unitized and stick-built systems.
Request Thermal Break Specifications
Get a detailed quotation for your curtain wall project including thermal break profile design, sealant specification, compatibility testing and factory quality control. Hanart delivers facades with certified joint performance for decades of service.
Specifications & Standards Referenced
- ASTM C1184
- ASTM C920
- ASTM D395
- ASTM C1087
- ASTM C794
- ASTM G155
- ASTM D2244
- ASTM D1149
Traceability & Sources
- Read the full source article: Sealants, Thermal Break Profiles & Curtain Wall Joint Performance — source page
- Project file: Asian Olympic Council Mansion, Kuwait — High-shade curtain wall with thermal break for 45-50 degree desert summers.
- Curtain Wall Water-Tightness in Extreme Climates — related note
- SSG Curtain Wall: Structural Glazing Explained — related note
- Facade Standards Hub — test methods cited across the library
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