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Dowsil 791 silicone weatherproofing sealant 500ml sausage for ±50% dynamic façade joint sealing
Dowsil 791 silicone weatherproofing sealant 500ml sausage for ±50% dynamic façade joint sealing

DOWSIL™ 791 Weatherproofing Sealant

Neutral-cure, non-sag silicone for weathersealing window perimeters, curtain walls and façades. Designed for durable exterior joints with ±50% movement capability; not for structural glazing.

Vendor: Dowsil
SKU: SILDC791BLK/SSG
Availability: In Stock
$14.97
$14.97
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Description  

DOWSIL 791 Weatherproofing Sealant is a neutral-cure, medium-modulus silicone for keeping window perimeters, curtain wall joints and building façades weather-tight. It remains flexible as architectural joints move and is designed to withstand long-term outdoor exposure.

Where to use DOWSIL 791

Specify 791 for non-structural weathersealing around aluminium window frames, glazing systems, curtain walls and façade connections. It suits properly designed vertical and overhead joints where a non-sag, durable weatherseal is needed.

What makes it suitable?

  • Purpose-built weatherseal: protects façade and glazing joints against weather rather than carrying structural loads.
  • ±50% movement capability: accommodates expansion and contraction in correctly designed joints.
  • Neutral cure: suitable for a broad range of commonly used glazing and façade materials, subject to adhesion and compatibility checks.
  • Non-sag application: stays in place during vertical and overhead joint sealing.
  • UV and weather resistance: suited to exposed building-envelope joints.

791 compared with 795

Choose DOWSIL 791 for weathersealing. If the joint must transfer structural loads from glazing or cladding, consider DOWSIL 795 only as part of an engineered, tested and approved structural system. The two products should not be treated as interchangeable on structural glazing projects.

Preparation and compatibility

Clean and dry the joint faces, remove contaminants and use suitable backing materials. Tool the sealant before a skin forms. Adhesion and compatibility testing is important for coated materials, porous surfaces and specialist façade systems; primer requirements vary by substrate.

Important limitations

  • Not a structural glazing adhesive.
  • Not suitable for below-grade or continuously submerged joints.
  • Do not install on wet or frost-covered surfaces or in enclosed joints without atmospheric moisture for curing.
  • Check compatibility with porous stone, plastics, coatings and materials that may bleed oils or plasticisers.
  • Cured silicone is not paintable.
Common Questions  

How much movement can Dowsil 791 accommodate?
It provides ±50% joint movement capability to ASTM C 719.

Can Dowsil 791 be used for structural glazing?
No. It is a weatherproofing sealant and should not be used as a structural sealant.

Can Dowsil 791 be painted?
No. Paint does not typically adhere to cured silicone.

Can Dowsil 791 be used below grade or under permanent water immersion?
No. It is not recommended for below-grade or continuously immersed applications.

Uses & Benefits  
Neutral-cure, non-sag silicone for general glazing and weather sealing in curtain walls, facades, perimeter joints and expansion joints. Accommodates ±50% joint movement to ASTM C 719. Service temperature range is -50°C to 150°C after cure. Resists sunlight, rain, snow and ozone and forms unprimed adhesion to most non-porous construction surfaces. Dowsil 791 is a weatherproofing sealant, not a structural glazing sealant.
How To Apply  
Clean joint surfaces to remove grease, oil, dust, water, frost, old sealant and protective coatings. Install the specified backing material, joint filler, setting blocks or spacer shims and mask adjacent surfaces where required. Apply Dowsil 791 in a continuous operation under positive pressure. Tool with light pressure within 15 minutes, before a skin forms, to press the sealant against the backing material and joint faces. Remove masking tape immediately after tooling. Full cure is typically 7 to 14 days at 25°C and 50% relative humidity, depending on joint depth and moisture access.
Limitations and Safety Info  
Do not use as a structural sealant. Do not use below grade or on surfaces under continuous water immersion. Do not apply when surface temperatures exceed 50°C. Do not apply to wet or frost-laden surfaces or in totally confined joints. 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 passed ASTM C 1248 non-stain evaluation. Do not use where the cured sealant must be painted. Do not use in direct food contact, medical or pharmaceutical applications.
Suitable Substrates  
  • Coated glass and glazing panels.
  • Galvanised steel and anodised architectural frames.
  • Masonry and precast concrete.
  • Other common porous and non-porous construction materials, subject to adhesion testing where required.

DOWSIL™ 791 Weatherproofing Sealant Physical Properties

DOWSIL™ 791 Weatherproofing Sealant Physical Properties
Property Value
Base Chemistry One-part, Neutral-cure RTV silicone
Colour Black
Curing System 7–14 days @ 25°C, 50% RH
Density 1.51 g/cm³
Consistency Non-sag (0 mm slump)
Tensile Strength 3.999 MPa (0.40 MPa after water immersion)
Elongation 430%
Movement Capability ±50%
Shore A Hardness 25–30
Pot Life 20 minutes
Full Cure 45 minutes @ 23°C, 50% RH
Application Temperature 4°C to 40°C
Service Temperature -50°C to 150°C
Coverage Rate 210 g/minute (flow rate)
VOC Content 45 g/L
Shelf Life 12 months (stored below 30°C)

DOWSIL™ 791 Weatherproofing Sealant - Use Cases

Here are some common examples on where DOWSIL™ 791 Weatherproofing Sealant used by our customers.

Civil Construction

High Movement Building Joints

When accommodating significant thermal expansion or structural movement in building expansion, connection, or perimeter joints.

Engineered for ±50% movement, it prevents joint failure and maintains integrity through extreme building movement cycles and harsh environmental exposure.

  • ±50% joint movement
  • ASTM C719
  • 120 Psi ultimate tensile
  • 430% elongation at break

Glazing

Facade Weather Sealing

Sealing exterior joints on curtain walls, precast panels, or building facades requiring durable weather protection.

This neutral-cure silicone delivers long-lasting, weather-resistant seals on diverse building materials, providing premium performance against water ingress.

  • ASTM C920 Class 50
  • ±50% joint movement
  • -50°C to 150°C service temp
  • neutral-cure silicone

Sheet Metal

Sensitive Substrate Perimeter Sealing

Sealing around metal panels, window frames, or coated glass in external building envelopes, requiring non-corrosive adhesion.

Its neutral-cure formulation suits weathersealing around selected frames and coated façade materials; verify adhesion and compatibility with the actual finishes before installation.

  • neutral-cure silicone
  • adheres to galvanised steel
  • adheres to coated glass
  • ASTM C920 Type S

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