Overview

Dowsil 791 Weatherproofing Silicone Sealant is a one-part, low modulus, neutral curing sealant designed for general glazing, and weather sealing in curtain walls & building facades ideal for both commercial and domestic applications. This exterior silicone sealant has exceptional weatherproofing properties it resists extreme temperatures, ozone and UV radiation. Versatile, it provides excellent adhesion to most porous and non-porous surfaces without needing a primer and cures to form flexible and durable joints.

• Ideal for general glazing applications
• Can be used for commercial & domestic applications
• Low odour
• Resists extreme temperatures, ozone & UV radiation
• Available in multiple colours
• Excellent unprimed adhesion to most porous and non-porous surfaces
• Conforms to ISO 11600-F&G-25LM and also meets ISO specification 9047 class 50%

Preparation

Ensure that all surfaces to be sealed are clean, dry, and sound. Surfaces should be free from frost, dust, grease, old sealants, and any other contaminants that could interfere with adhesion.

• For non-porous surfaces (such as glass, aluminum, or metal), clean and degrease the area using a suitable solvent, such as DOWSIL™ R-40 Universal Cleaner. Apply the cleaner on a clean, lint-free cloth, and wipe down the surfaces thoroughly to remove any oils, dust, or other residues. Allow the surfaces to dry completely before application.
• For porous surfaces (like concrete, brick, or mortar), use mechanical cleaning methods to remove loose particles and contaminants. A steel brush, sanding disc, or other appropriate tools can be used to clean these surfaces effectively.
• DOWSIL™ 791 is designed for good adhesion to most common substrates. However, due to the variety of coatings and finishes that can affect adhesion, it is recommended to test adhesion on a small, inconspicuous area before applying the sealant to the entire joint.
• For optimal adhesion, especially when working with porous surfaces, priming may be required. A primer will help maximize the sealant's adhesion.
• Mask areas adjacent to the joint with tape to prevent contamination of the substrates and to ensure a clean, neat sealant line. It is essential to remove the masking tape immediately after tooling the sealant to achieve a professional finish.
• Always ensure adequate ventilation when using cleaning solvents or when working in confined spaces. Follow all safety precautions as indicated on the solvent labels. Wear solvent-resistant gloves, goggles, and protective clothing as needed.

Application

When back-up material is necessary, use a closed-cell polyethylene backer rod. For joints too shallow for backer rods, use low tack polyethylene tape. Back-up materials provide back pressure and prevent three-sided adhesion, which could limit the sealant’s movement capability.

• Apply DOWSIL™ 791 Weatherproofing Silicone Sealant in a continuous bead using an appropriate sealant gun such as Geocel Cox Skeleton Gun. Ensure a positive pressure is maintained throughout the application for consistent and even coverage. The sealant should be applied to the joint or gap without interruption.
• After application, tool the sealant within 5 minutes to ensure good contact between the sealant and the substrate. Tooling also helps achieve a smooth, professional finish for best results use Bedec Silicone Profilers. The surface should be tooled lightly, ensuring the sealant is pressed into the joint without overworking it.
• Any excess sealant should be cleaned off tools and non-porous surfaces while still in an uncured state using DOWSIL™ R-40 Universal Cleaner. For sealant that has been misapplied to porous surfaces, it should be left until just cured, and then it can be removed using peeling, cutting, or other mechanical means. Be careful not to damage plastic or coated surfaces.
• The width and depth of the joint must accommodate the movement capability of the sealant. Ensure the joint width is designed with the following guidelines.
• Joints between 6-12mm: Seal depth should be 6mm.
• Joints above 12mm: Use a width-to-depth ratio of 2:1. For situations where fillet joints are needed, ensure a minimum of 6mm sealant bite on each substrate.
• Remove masking tape immediately after tooling to prevent it from adhering to the sealant and to achieve a clean edge. Ensure the sealant has been properly tooled before removing the tape to avoid damaging the joint.
• Allow the sealant to cure according to the product’s specifications. Curing time will depend on factors such as joint size, ambient temperature, and humidity levels. Be sure to keep the joint undisturbed during the curing process.

Always follow manufacturers instructions found on the packaging.

Aftercare & Storage