Dowsil 791 Weatherproofing Sealant

DOWSIL 791 Weatherproofing Sealant is a one-part, neutral-cure silicone designed specifically for window perimeter sealing, curtain wall weathersealing, façade joints and other high-movement exterior joints. With ±50% movement capability and excellent resistance to sunlight, rain, snow and ozone, it is a strong choice where the primary job is to keep an architectural joint weather-tight over long-term movement and exposure.

For glazing and façade contractors, the key distinction is simple: DOWSIL 791 is a weatherproofing sealant, not a structural glazing adhesive. It seals around glazing systems, aluminium frames, curtain wall assemblies and façade interfaces, while structural glass bonding should use an approved structural glazing product such as DOWSIL 795 where the complete system has been designed and approved for that purpose.

Silicone weatherproofing sealant for windows, curtain walls and façades

DOWSIL 791 is suited to general glazing and building-envelope weathersealing where joints must remain flexible through thermal and building movement. Typical applications include window and door perimeter joints, curtain wall weatherseals, façade expansion and connection joints, aluminium framing, precast interfaces and other architectural perimeter joints.

Why choose DOWSIL 791?

• ±50% movement capability: accommodates substantial extension and compression in correctly designed joints.
• Purpose-built weathersealing: developed for general glazing, curtain wall and building façade weatherseal applications.
• Neutral cure: suitable for a wide range of sensitive construction substrates including coated glass, galvanised steel and masonry.
• Excellent weatherability: highly resistant to sunlight, rain, snow and ozone.
• Medium-modulus performance: balances flexibility with a stable cured profile for architectural movement joints.
• Non-sag application: suitable for vertical and overhead joints.
• Service temperature: -50°C to +150°C after cure.
• Working time: approximately 20 minutes at 23°C and 50% relative humidity.
• Tack-free time: approximately 45 minutes at 23°C and 50% relative humidity.
• Cure time: typically 7 to 14 days at 25°C and 50% relative humidity, depending on joint dimensions and conditions.

Compatible substrates

DOWSIL 791 is designed for use across common façade and glazing materials including glass, coated and reflective glass, aluminium, anodised aluminium, fluorocarbon-coated aluminium, stainless steel, steel, metal panels, brickwork, concrete, masonry, granite, limestone, stone, painted surfaces, selected plastics and PVC-U. Primer is generally not required on many non-porous surfaces, but adhesion testing should be carried out and some porous or difficult substrates may require primer.

Joint preparation and application

Joint surfaces must be clean, dry and free from grease, oil, dust, frost, water, old sealant and protective coatings. Install the specified backing material, joint filler, setting blocks, spacer shims or tapes before sealing. Apply DOWSIL 791 continuously under positive pressure and tool the bead before a skin forms so the silicone fully contacts the joint faces and backing material.

Apply between 4°C and 40°C. Correct joint design, backing material and substrate preparation are essential to long-term weatherseal performance.

DOWSIL 791 vs DOWSIL 795

Choose DOWSIL 791 when the primary requirement is architectural weathersealing. It is the dedicated choice for window perimeters, curtain walls, façade joints and other movement joints that do not carry structural glass loads.

Choose DOWSIL 795 when the project involves structural glazing or structural attachment and the complete system has been reviewed and approved for that application.

Important limitations

• Do not use DOWSIL 791 as a structural glazing sealant.
• Do not use below grade or on surfaces continuously immersed in water.
• Do not apply when the substrate surface temperature exceeds 50°C.
• Do not apply to wet or frost-covered surfaces.
• Do not use in totally confined joints where atmospheric moisture cannot reach the sealant.
• Do not use on materials that bleed oils, plasticisers or solvents, or on green or partially vulcanised rubber gaskets or tapes.
• Do not use on natural stone unless the substrate has been approved or has passed appropriate non-stain testing.
• Do not use where the cured silicone must be painted.

For other window, shopfront and glazing-perimeter options, browse our Window, Shopfront & Perimeter Weatherseal range.