Dow Corning® 123 Silicone Seal is a specialized product designed for use as a bridge joint in construction and restoration projects. It is a preformed, low modulus silicone extrusion that offers versatility in sealing applications where flexibility and durability are essential. The product is suitable for a wide range of substrates and environments, particularly in scenarios requiring the restoration of failed sealant joints. This article provides a comprehensive overview of the installation and application procedures for Dow Corning® 123 Silicone Seal, drawing on information from the official technical documentation provided by the manufacturer.
Overview of Dow Corning® 123 Silicone Seal
Dow Corning® 123 Silicone Seal is a low modulus silicone extrusion that is preformed for use in bridge joints. It is engineered to accommodate movement and stress in construction joints, making it ideal for applications where substrates may expand, contract, or shift due to environmental or mechanical forces. The product is available in widths ranging from 1 inch (25 mm) to 12 inches (300 mm), and can be customized in shape and color to suit specific project requirements.
The seal is designed to work in conjunction with other Dow Corning silicone-based sealants, such as Dow Corning® 795, 791, 756 SMS, and 758 Silicone Sealants, which may be used as adhesives or weatherproofing agents depending on the application. These sealants are selected based on the sensitivity of the substrates involved, with a focus on minimizing staining, residue, and streaking. For example, the 756 SMS Building Sealant is recommended for weathersealing sensitive substrates such as porous natural stone and glass facades, while the 758 Silicone Weather Barrier Sealant is suitable for use with low-energy surfaces like sheet or peel-and-stick weather-resistant barriers.
Key Considerations for Joint Sizing and Movement Capacity
One of the critical aspects of using Dow Corning® 123 Silicone Seal is determining the appropriate joint width and movement capacity. The seal is designed to accommodate movement caused by thermal expansion and live loading. The width of the joint can be calculated using the formula:
$$ \text{Minimum Joint Width} = \frac{100}{X} (Mt + Ml) + T $$
Where: - $ X $ is the sealant movement capacity in percentage - $ Mt $ is the movement due to thermal expansion - $ Ml $ is the movement due to live loading - $ T $ is the construction tolerance
For example, in a horizontal joint between an aluminum curtainwall and a concrete panel with a thermal movement of 5/16 inch (8 mm), a live load movement of 1/4 inch (6 mm), and a construction tolerance of 1/4 inch (6 mm), the required width using a 25% movement capacity sealant would be 2 1/2 inches (62 mm). This calculation ensures that the joint is wide enough to accommodate all expected movements without compromising the integrity of the seal.
Surface Preparation and Joint Cleaning
Proper surface preparation is essential for ensuring the long-term performance of Dow Corning® 123 Silicone Seal. The joints must be thoroughly cleaned to remove any contaminants, impurities, or residues that could interfere with adhesion or the sealant’s ability to function effectively. The following steps are recommended for joint preparation:
Cleaning: Use a wire brush (either power or hand-operated), grinding, saw cutting, or solvent cleaning to remove all contaminants from the joint to the depth where the new sealant and backer rod will be installed. It is important to ensure that the joint is free of dust, loose particles, and any other debris that could compromise the seal.
Air Blasting: After cleaning, use moisture-free and oil-free compressed air at a pressure of 6.0 kg/cm² to blow out any remaining dust or loose particles. In some cases, a second pass with a wire brush and air blast may be necessary to ensure the joint is fully clean.
Drying and Inspection: The joints must be completely dry, dust-free, and free of frost before applying the sealant. Any loose pieces of caulk or backer rod lodged in the joint should be removed to prevent future issues.
Masking: If applicable, mask the edges of the joint to facilitate application and cleanup.
Application Procedures for Structural Sealant Joints
The application process for Dow Corning® 123 Silicone Seal is designed to ensure that the sealant is properly installed and functions as intended. The following steps outline the general procedure:
Cleaning and Priming: Joint surfaces must be clean, dry, dust-free, and frost-free. If priming is required based on testing, the primer should be applied to the cleaned surfaces. This step is particularly important for surfaces that may have low adhesion properties or are known to resist bonding.
Applying the Sealant: The sealant is applied by "pushing the bead" into the structural joint cavity. This method ensures that the sealant fills the joint uniformly and creates a solid bond with the surrounding materials.
Tooling the Sealant: Once the sealant is in place, it should be tooled to ensure that it wets out and contacts both sides of the joint as well as the spacer. This step helps eliminate voids and ensures that the sealant forms a continuous, even surface.
Creating a Flush Joint: Dry tooling techniques should be used to create a flush joint. This helps to ensure that the sealant has the proper configuration and fully contacts the joint walls.
Verification and Testing: Field adhesion tests are recommended to confirm that the sealant adheres properly to the substrates. These tests are part of the quality assurance process and help ensure that the sealant will perform as expected in real-world conditions.
Weatherproofing Joints and Sealant Application
In addition to structural sealant joints, Dow Corning® 123 Silicone Seal may also be used in weatherproofing applications. The application procedure for these joints follows a similar set of steps but with additional emphasis on ensuring that the sealant is applied correctly to prevent water infiltration and other environmental issues.
Clean the Joint Surfaces: Joint surfaces must be clean, dry, dust-free, and frost-free. Any contaminants that could interfere with adhesion should be removed.
Apply Primer if Required: Depending on the surface and the test results, a primer may be applied to improve adhesion. This is especially important for surfaces that are difficult to bond to or that have low surface energy.
Install Backer Rod or Bond Breaker: If necessary, backer rod or bond breaker is installed to support the sealant and prevent it from adhering to the wrong areas.
Apply the Sealant: The sealant is applied into the joint cavity using the recommended method. It is important to ensure that the sealant is applied in a continuous, even bead.
Tool the Sealant: Dry tooling techniques are used to create a flush joint and to ensure that the sealant has the proper configuration and fully contacts the joint walls.
Verify Sealant Performance: Field adhesion tests are conducted to verify that the sealant has bonded properly and that it will perform as expected in the intended environment.
Special Considerations for Repair and Restoration Projects
When using Dow Corning® 123 Silicone Seal in repair or restoration projects, it is important to follow specific procedures to ensure that the sealant is applied correctly and that it functions as intended. These procedures are particularly relevant if the original sealant was a Dow Corning product and the original recommendations are still available.
Conduct a Field Adhesion Test: Before beginning the repair, a field adhesion test should be performed to confirm that the existing silicone adheres properly to the substrates. If excellent adhesion is not observed, contact a Dow Corning representative for further guidance.
Deglaze the Area: Depending on the joint design, deglazing may require the use of specially designed tools or piano wire to cut behind the silicone. This step is important to ensure that the area is properly prepared for the new sealant.
Cut or Remove the Existing Sealant: The existing sealant should be cut away, leaving a thin film (approximately 0.02–0.04 inches or 0.5–1 mm thick) of adhesive on the frame. If the surface finish of the substrate is to be preserved, care must be taken to avoid damaging it. Alternatively, all sealant can be removed, but this should be done with caution to prevent damage to the substrate.
Clean the Residual Sealant: The residual sealant should be cleaned using a solvent and the "two-cloth" cleaning technique. If fresh sealant will be applied immediately after cutting the cured sealant, cleaning may not be necessary. However, if the sealant has been completely removed, primer may be required to ensure proper adhesion.
Allow Solvent to Evaporate: If the existing sealant has absorbed some solvent, it should be allowed to evaporate completely before applying the new sealant. This ensures that the surface is dry and ready for the new material.
Apply Fresh Sealant: Fresh sealant can adhere to cured sealant without the need for primer. However, if the sealant has been completely removed, primer may be necessary to ensure a strong bond.
Safety and Warranty Information
Dow Corning® 123 Silicone Seal is a product that requires careful handling and application to ensure its effectiveness and longevity. The manufacturer provides a limited warranty that covers the product’s conformance to the specifications in effect at the time of shipment. However, the warranty does not extend to incidental or consequential damages, nor does it imply that the product is suitable for a specific purpose or application.
The information provided in the technical documentation is based on the best available knowledge at the time of publication. However, because conditions and methods of use can vary, it is the responsibility of the user to conduct tests to ensure that the product is safe, effective, and suitable for the intended use. Suggestions for use should not be interpreted as an inducement to infringe on any patent.
Conclusion
Dow Corning® 123 Silicone Seal is a versatile and durable product designed for use in a wide range of construction and restoration applications. Its low modulus properties make it well-suited for joints that are subject to movement and stress, and it can be used in conjunction with other Dow Corning sealants to achieve optimal performance. Proper installation and application are critical to ensuring that the seal functions as intended and provides long-term protection against environmental factors such as water, wind, and temperature fluctuations.
By following the manufacturer's guidelines for surface preparation, joint cleaning, sealant application, and quality assurance, users can ensure that their projects meet the highest standards of performance and durability. Whether used in new construction or in repair and restoration efforts, Dow Corning® 123 Silicone Seal is a reliable choice for professionals and DIY users alike.