In modern façade and glazing systems, joint design plays a crucial role in structural integrity and long-term performance.
Dowsil 895 Structural Glazing Sealant is one of the world’s most trusted silicones for bonding glass and metal, offering unmatched adhesion and durability when applied correctly.
This guide explains how to design, prepare, and install Dowsil 895 joints for structural glazing applications — ensuring strength, flexibility, and reliability that meet professional standards.
What Is Dowsil 895?
Dowsil 895 is a one-part, neutral-cure silicone formulated specifically for structural glazing.
It provides long-term adhesion between glass, metal, and other façade materials, maintaining elasticity under wind load, thermal movement, and weathering.
Key Features:
Neutral-cure silicone – non-corrosive to metals
High tensile and peel strength for structural bonding
Excellent UV, ozone, and weather resistance
Movement capability ±25 % (ISO 11600 F-25LM)
Compatible with glass, anodised aluminium, and coated metals
When used as part of a properly engineered joint system, Dowsil 895 can last for decades under severe environmental conditions.
Understanding Structural Joint Design
Unlike conventional weather seals, structural silicone jointscarry load. They must be dimensioned precisely to managedead load (glass weight) and wind loadsafely.
A typical Dowsil 895 joint serves two functions:
Bonding:Transfers structural loads from glass to frame.
Sealing: Provides a watertight barrier against the elements.
Proper design ensures the sealant performs both roles without overstressing the material.
Key Design Parameters for Dowsil 895 Joints
Joint Thickness
Minimum: 6 mm for structural applications
Typical range:6 – 12 mm, depending on glass size and load
The thickness must allow movement without exceeding 20 % strain in the sealant.
Bond Width
Width is critical for load transfer.
Generally between 10 – 15 mm, calculated based on glass weight, panel size, and design wind load.
Must maintain a minimum bond areaof 6 mm × 10 mm for standard façade conditions.
Aspect Ratio (Width : Thickness)
Should not exceed 2 : 1 — a balance between strength and flexibility.
Edge Bite (Structural Engagement)
Recommended minimum 6 mm bite on glass edge.
Greater bite may be required for large or heavy panels.
Movement Accommodation
Dowsil 895 is rated ±25 % movement.
Ensure frame design allows this without overstressing the seal.
Substrate Preparation & Priming
For structural joints, surface preparation is critical.
Cleaning:Use Dowsil R-40 or compatible solvent cleaner. Remove dust, grease, and oxidation.
Priming: Depending on substrate, a Dowsil primer may be required to achieve full adhesion (e.g., Primer P or 1200 OS).
Testing: Always perform adhesion tests before full application — particularly on coated or anodised substrates.
Application & Setup Best Practices
Masking:Apply masking tape to maintain clean joint lines.
Backer Rod:Use closed-cell polyethylene rod to control sealant depth.
Application: Extrude Dowsil 895 smoothly using a pneumatic or manual gun.
Tooling: Tool immediately to ensure full wetting of the bond surfaces.
Curing:
Skin formation in ~30 minutes.
Full cure achieved in 7–14 days (depending on joint depth and ambient conditions).
Avoid stressing the joint during cure
Quality Control & Testing
Before installation, it’s standard to carry out:
Adhesion tests: Confirms primer compatibility.
Cohesion tests: Ensures internal strength of cured silicone.
Movement simulation:Checks performance under design loads.
Dowsil provides specific project-by-project validation and technical datasheets outlining minimum bond dimensions for given glass and frame sizes — always consult these before design approval.
Common Mistakes to Avoid
❌ Using acetoxy silicones (incompatible with metals).
❌ Poor surface cleaning leading to bond failure.
❌ Applying too thin a joint — insufficient load capacity.
Navigation
