Dow Corning 795 Silicone Building Sealant is a versatile, one-part, medium modulus, neutral-curing silicone sealant designed for structural glazing and weathersealing applications. With a wide range of color options, it is ideal for both functional and aesthetic sealing needs in construction and building maintenance. The sealant is particularly useful in applications where long-term durability and minimal staining are required, such as in glass facades, porous natural stone, and panel systems. This article provides a comprehensive overview of the installation process, application methods, storage conditions, and surface preparation requirements based on the available technical documentation.
Overview of Dow Corning 795 Silicone Building Sealant
Dow Corning 795 is a neutral-curing silicone sealant that offers medium modulus, meaning it has a balance of flexibility and strength. It is suitable for both structural and weathersealing applications and is available in a wide variety of colors, making it adaptable to diverse architectural designs. The sealant is recommended for use in areas where aesthetic performance is important, such as skylights, glass facades, and panel systems, where staining and residue rundown streaking must be minimized.
The sealant is part of a broader family of silicone-based products offered by Dow Corning, which includes other sealants such as 791, 756, and 758, each tailored for specific applications. The 795 variant is particularly noted for its ability to bond to a variety of substrates, including glass, metal, and stone, without causing discoloration or degradation over time.
Surface Preparation
Proper surface preparation is crucial for ensuring the long-term adhesion and performance of Dow Corning 795. The surfaces must be clean, dry, and free of frost, dust, oil, and other contaminants. The documentation specifies that surfaces should be prepared using a solvent wipe or a combination of solvent wipe and 1200 OS (a primer or adhesive promoter). This method ensures that the surface is free of any substances that could interfere with the adhesion of the sealant.
In some cases, especially with difficult-to-reach areas or rough surfaces, a clean brush may be used to apply the primer. However, over-priming is discouraged, as it can lead to adhesion loss. If too much primer is applied, a powdery or chalky film may form on the surface, which should be removed using a clean, dry, lint-free cloth or a nonmetallic bristle brush.
Masking tape should also be applied to adjacent surfaces to prevent the sealant or primer from spreading to unintended areas. This is particularly important when working with porous substrates or surfaces that are sensitive to chemical exposure.
Primer Application
Dow Corning recommends the use of specific primers for certain substrates to enhance adhesion and ensure a durable bond. The primer should be applied only to surfaces that have been properly cleaned and are completely dry. The application process involves pouring the primer into a small, clean container, ensuring that the cap is replaced and tightened to prevent contamination from atmospheric moisture. It is important not to pour more than a 10-minute supply at a time to maintain the integrity of the primer.
The preferred method of application is to use a clean, dry, lint-free cloth to gently wipe a thin film of primer onto the surface. For rough or irregular surfaces, a clean brush may be used to apply the primer in a thin, even layer. The primer should be allowed to dry completely, with the solvent evaporating within 5 to 30 minutes, depending on temperature and humidity.
After the primer has dried, the surface should be inspected for any residual film. If a powdery or chalky film is present, it indicates over-priming, and the excess should be removed. The surface is now ready for the application of the sealant.
Sealant Application
Once the surface is properly prepared and primed, the Dow Corning 795 Silicone Building Sealant can be applied. The sealant should be applied in a continuous operation to ensure that the joint is properly filled and sealed. The joint depth should be maintained according to the design specifications, and a backup material should be installed to the appropriate depth to support the sealant.
The sealant should be applied using a blunt instrument or a dry tool to shape the joint slightly concave. Tooling should be done immediately after the sealant is applied to ensure proper shaping and adhesion. The use of a masking tape or other temporary material may be necessary to maintain the desired shape during the curing process.
A test joint should be sealed to verify adhesion after the sealant has cured for 7 to 21 days. This step is important to ensure that the sealant has bonded properly and will perform as expected under real-world conditions.
Storage and Shelf Life
Dow Corning 795 has a specific shelf life and storage requirement to maintain its performance and integrity. The sealant must be stored at temperatures below 27°C (80°F). The "use by" date is clearly marked on the product packaging, and it is important to follow this date to ensure the sealant remains effective.
Proper storage is essential to prevent premature curing or degradation of the sealant. Exposure to high temperatures or direct sunlight should be avoided, as these conditions can reduce the working time and affect the sealant's ability to cure properly.
Compatibility with Substrates
Dow Corning 795 is compatible with a wide range of substrates, including glass, metal, and porous natural stone. It is particularly suitable for applications involving sensitive materials where staining and residue rundown streaking must be minimized. The sealant is also recommended for use with Corten steel, although special considerations may be necessary due to the potential for ongoing corrosion at the bond line.
In applications involving Corten steel, it is important to note that continued corrosion of the steel at the bond line can lead to the disintegration of the underlying substrate. This is excluded from the limited weathersealing warranty, and it is recommended that high-performance coatings or primers be used to inhibit corrosion. Dow Corning advises contacting coating manufacturers for recommendations and can perform adhesion testing on cured samples of specified coatings to ensure compatibility.
Troubleshooting and Common Issues
Despite the robust formulation of Dow Corning 795, certain issues may arise during installation or after application. These can include adhesion failure, excessive shrinkage, or discoloration. Adhesion failure is often the result of improper surface preparation or over-priming. To address this, it is important to follow the recommended surface preparation steps and avoid applying excessive primer.
Excessive shrinkage can occur if the sealant is not applied in a continuous operation or if the joint depth is not properly maintained. To minimize shrinkage, the sealant should be applied in a uniform manner, and the joint should be shaped to the appropriate depth using a backup material.
Discoloration or staining may occur if the sealant is applied to a substrate that is not fully compatible or if the surface is not properly cleaned. In such cases, it is recommended to use a primer or coating that is specifically designed for the substrate to ensure long-term durability and aesthetic performance.
Safety and Compliance
Dow Corning 795 is a neutral-curing silicone sealant, which means it does not emit harmful byproducts during the curing process. This makes it suitable for use in indoor environments and applications where air quality is a concern. The sealant is also compliant with various industry standards and regulations, ensuring its suitability for use in construction and building maintenance.
When handling the sealant, it is important to follow standard safety precautions, such as wearing gloves and eye protection. The sealant should be stored in a well-ventilated area, and any unused material should be disposed of according to local regulations.
Conclusion
Dow Corning 795 Silicone Building Sealant is a high-performance, one-part silicone sealant designed for a wide range of structural and weathersealing applications. Its medium modulus and neutral-curing properties make it ideal for use in environments where both durability and aesthetics are important. The sealant is compatible with a variety of substrates, including glass, metal, and porous natural stone, and is available in a wide range of colors to match architectural designs.
Proper installation and application are essential to ensure the long-term performance of the sealant. This includes thorough surface preparation, correct primer application, and adherence to recommended storage and handling guidelines. By following these procedures, contractors and DIY users can achieve a durable, aesthetically pleasing seal that meets the requirements of both functional and decorative applications.