How to weatherproof a glass facade?

One of the last steps in installing glass curtain walling is creating a weathertight barrier against air and water infiltration between glass panels. Sealing the joints with a silicone sealant is a critical process that ensures the glass curtain wall’s structural integrity, weather resistance, and long-term durability. A properly sealed curtain wall also helps to improve the building’s energy efficiency by reducing air leakage and heat transfer.

For professional builders, sealing glass curtain walls is a critical final task that demands precision, expertise, and the right choice of materials. The builders must adhere to local and project-specific standards when choosing a sealant for curtain walls (e.g., ASTM, EN). In Penosil product range we have a few sealants for sealing glass curtain walls, such as Penosil Facade & Glazing Silicone 340/340c. It is a neutral alkoxy-cure silicone developed specifically for facade weatherproofing and glazing applications.

Why use neutral silicone for sealing glass curtain walls instead of other types of sealants? Well, compared to other types of sealants, the neutral cure sealants such as alkoxy and oxime silicones offer a non-corrosive cure. This means that neutral silicones can be used in contact with aluminium and other most common curtain walling materials, without damaging them or degrading the sealant joint. Metals, laminated glass and some glazed surfaces are not always compatible with other types of sealants. Also, neutral silicones are totally UV proof and have extremely long service life which makes them perfect for facade works. Even though neutral silicones can be used in contact with many materials, we always recommend performing a compatibility test with adjacent materials, such as the glass, aluminium frames, and other components before starting the work.

Neutral alkoxy silicone forms a strong bond between glass and frame, and ensures a durable seal that is weather-, UV and ageing resistant. The non-sagging and permanently elastic formula of Penosil Facade & Glazing Silicone 340/340c has been specifically developed for sealing vertical and horizontal facade joints. Its high movement capability (±25%) accommodates the movements of the curtain wall components due to temperature changes and other factors, preventing cracks and maintaining the integrity of the seal. This versatile product comes in ten different colour options and can also be used for other types of facade works such as weatherproofing joints between concrete facade panels, sealing window and door perimeter joints, and glazing works.

How to apply Penosil Facade & Glazing Silicone 340/340c?

• Clean all surfaces thoroughly. Ensure surfaces are dry, free from dust, grease, loose particles, etc. Non-porous surfaces (e.g., glass, aluminium) should be wiped with solvent and a clean cloth. To avoid adhesion issues, solvent residue must be removed before evaporation.
• Protect the adjacent surfaces with masking tape. Using masking tape helps to achieve clean joint lines and prevent sealant from spreading on glass.
• Typical joint width-to-depth ratio is 2:1. However, we always recommend following project specifications, and glass unit manufacturer’s guidelines. In deeper joints, use a backer rod behind the joint to control sealant depth and prevent three-sided adhesion. If the sealant is not supported by backer rod, the sealant joint might fail over time.
• Ensure that the exterior temperature is compatible with the sealant’s application temperature range (Penosil Facade & Glazing Silicone 340 application temperature range is 5°C to 40°C).
• Cut the tip of the cartridge, screw on the nozzle and trim it at a 45° angle which is slightly larger than the joint to be sealed. Place the cartridge into a sealant gun.
• Apply the sealant by keeping an even pressure at the gun trigger and smoothly dragging the nozzle along the joint, ensuring a continuous, even bead without air bubbles or gaps. Make sure the sealant bead has full contact with both sides of the joint.
• Remove the excess sealant and smooth the surface with a suitable tool. Tooling helps to achieve a smooth, even finish and ensure full contact with the substrates. Tooling must be done before skin formation begins (skin formation time for Penosil Facade & Glazing Silicone 340 is 15–20 min).
• Check that the sealant joint is complete with no voids or discontinuities. Inspect for proper drainage slopes at the edges to prevent water accumulation. If everything is perfect, remove masking tape immediately after tooling and if needed clean the excess uncured silicone with solvent.
• During the curing process, protect the sealant from impurities and verify that the joint surface is not affected by mechanical load. The sealant curing time depends on the temperature, humidity levels and joint size. Penosil Facade & Glazing Silicone 340 curing rate is 2.5–3.5 mm per 24 hours.
• Regularly inspect the condition of the sealant joints to identify any signs of damage or degradation. If damage has occurred, repair or replace the sealant in the affected joint immediately to maintain the weathertightness and structural integrity of the curtain wall. 

To succeed in sealing glass curtain walls, it is important to use high-quality silicone sealants specifically formulated for structural glazing applications and weatherproofing. By following the sealant manufacturer’s recommendations for correct joint design, application techniques and thorough inspection protocols, professional builders can deliver glass facades that are both weatherproof and visually striking.