Building facades endure constant movement and weather exposure. Getting the weather seal right prevents future call-backs and costly water ingress. DOWSIL 791 delivers robust, premium performance weather sealing for critical expansion, connection, and perimeter joints. This neutral-cure silicone sealant offers significant movement capability and long-term durability, ensuring the integrity of curtain walls and building envelopes.

Why this product exists

DOWSIL 791 is formulated as a workhorse weather sealant for high-performance building envelopes. It's engineered to accommodate the dynamic forces exerted on facades, including thermal expansion, wind load deflections, and building settlement. This neutral-cure RTV silicone forms a flexible, durable rubber seal that stands up to harsh environmental conditions, providing peace of mind for architects and contractors needing reliable, long-lasting weather protection.

The numbers that matter

  • ±50% Movement Capability: This means a 20mm joint can reliably expand or contract by 10mm without failing. This high movement rating is critical for accommodating the significant thermal and structural shifts common in modern facades, preventing stress-induced sealant fatigue and subsequent water ingress.
  • -50°C to 150°C Service Temperature: DOWSIL 791 maintains its elasticity and performance across extreme temperature fluctuations. From sub-zero winters to scorching summers, the sealant remains functional, preventing embrittlement or softening that can lead to joint failure.
  • 430% Elongation at Break: This high elongation value provides a substantial safety margin beyond the rated movement. It indicates the sealant's capacity to stretch significantly before breaking, offering resilience against unexpected or extreme joint movements.
  • Neutral Cure: The neutral-cure chemistry ensures compatibility with sensitive substrates like coated glass, galvanised steel, and other painted or anodised metals. This prevents the corrosion, discolouration, or etching that acidic-cure silicones can cause, protecting the aesthetic and structural integrity of the facade materials.

What it's like to use

DOWSIL 791 extrudes easily and offers a 20-minute working time, allowing for precise application and tooling across complex joint geometries. Its tack-free time of 45 minutes provides sufficient window for final adjustments before skinning. For optimal performance and to prevent three-sided adhesion, always install a compatible backer rod to control sealant depth. While primer is often not required on non-porous surfaces, a test placement is recommended, and an appropriate primer should be used on certain porous substrates for optimal adhesion. Tool the sealant within 15 minutes of application, then remove masking tape immediately for clean lines.

Where this product excels

DOWSIL 791 is purpose-built for the rigorous demands of exterior building applications where movement and weather exposure are constants.

  • Curtain Walls and Building Facades: Its high movement capability and weather resistance make it ideal for sealing panel joints, perimeters, and connections, maintaining weather integrity against wind, rain, and UV radiation.
  • Perimeter Sealing of Windows and Doors: Provides a durable, flexible seal around fenestration, accommodating thermal expansion and contraction between different building materials.
  • Precast Concrete and Masonry Panel Joints: Offers excellent adhesion and movement for large precast elements, ensuring the long-term weatherproofing of concrete structures.
  • Metal Cladding and Roofing Expansion Joints: Neutral cure prevents corrosion on sensitive metal finishes, while its flexibility handles the significant expansion and contraction of metal panels.

Choose this when

  • When a project demands a premium, high-movement weather sealant for building facades.
  • When sealing expansion, connection, or perimeter joints in curtain walls, windows, or doors.
  • When working with sensitive substrates like coated glass, galvanised steel, or anodised aluminium where neutral cure is critical.
  • When long-term UV stability and resistance to extreme weather conditions are non-negotiable.

Don't use this when

  • Not for: Structural glazing applications. For structural bonding, consider Dowsil 795 Silicone Sealant.
  • Not for: Continuously immersed conditions or below-grade applications.
  • Not for: Surfaces that will be painted. Silicone sealants are generally non-paintable.
  • Not for: Totally confined joints, as the sealant requires atmospheric moisture to cure.
  • Not for: Natural stone unless ASTM C1248 non-stain testing has been conducted and approved.

DOWSIL 791 is independently tested and complies with key international standards including ASTM C920 Type S, Grade NS, Class 50, Use NT, M, G, A. This classification confirms its suitability for various non-sag applications, including pedestrian and vehicular traffic (NT), masonry (M), glass (G), and aluminium (A), with a high-movement capability.

DOWSIL 791 vs. DOWSIL 795: Know the difference

While both DOWSIL 791 and DOWSIL 795 are high-performance silicone sealants for building applications, their primary use cases differ significantly. DOWSIL 791 is specifically engineered as a premium weatherproofing sealant for facade joints, offering exceptional movement and weather resistance. It is the go-to for sealing expansion, connection, and perimeter joints where preventing water ingress is paramount. In contrast, Dowsil 795 Silicone Sealant is a dedicated structural glazing sealant, designed for applications where the sealant bears a structural load, such as bonding glass or panels to a frame without mechanical fasteners. Do not interchange these products. Select DOWSIL 791 for robust weather seals, and DOWSIL 795 when structural performance is required.