Silicone sealants are used for a variety of purposes – from major construction projects to simple home fixes. Knowing how to properly caulk with silicone sealant can save you a lot of problems in the long-term because when done correctly, it requires very little maintenance or repairs.

In this article, we will give you a step-by-step guide to applying silicone sealant perfectly in a structural glazing application to ensure a smooth finish that will last for years to come.



Step #1: Cleaning

Proper surface preparation is extremely important to the longevity and performance of silicone sealants. Cleaning is the first step to ensuring that you have a dirt-free, dust-free, oil-free, and optimal substrate for the sealant to develop adhesion to.

Cleaning with Isopropyl Alcohol (IPA)


  1. Isopropyl alcohol (IPA) is the recommended solvent for cleaning metal and glass intended for structural glazing applications.
  2. The solvent acts as a degreaser to remove the cutting oils and other contaminants used in the fabrication of the framing system. The solvent must be clean and fresh and must comply with local occupational safety codes. When used indoors, such as in a factory environment, proper ventilation must be provided.
  3. Cloths used for cleaning of all framing members should be white, lint free and resistant to the recommended solvent. Do not use chemically treated rags.
  4. Pour the approved solvent onto a clean, dry cloth. Do not place cleaning cloth into the solvent solution container. This prevents solvent contamination, which can lead to a sealant adhesion problem. Vigorously rub the glass and metal surfaces to remove the contaminants. Continuously rotate the cloth, lifting off the oils loosened by the solvent.

Dry cloth cleaning


  1. Do not allow the solvent to air dry during the cleaning procedure. After the solvent wipe, follow immediately with another clean dry cloth to wipe the surface dry (2-rag method). Allowing the solvent to dry on the surface without wiping with a second cloth negates the entire cleaning procedure because the contaminants are redeposited as the solvent dries.
  2. When cleaning deep, narrow joints, wrap the cleaning cloth around a clean, narrow-blade putty knife. This permits force to be applied to the surface to be cleaned.
  3. Clean only as much area as can be sealed in 1 hour. If cleaned areas are exposed to contaminants (oils, dirt, dust, etc.), the surface must be cleaned again.
  4. Keep solvent containers closed when not in use. Temperature and humidity will affect the evaporation rate of the applied solvent therefore affecting its cleaning power.

Caution:

  • Never use a paintbrush for the cleaning procedure. It is not effective in removing the contaminants off the surface. The rubbing action of the cloth is critical and essential for loosening up the contaminants from the substrate.


Step #2: Priming

Primers promote strong and consistent adhesion of the silicone sealant to the substrates to which it may otherwise be difficult to bond. If required to use primers in structural glazing applications, we recommend following these few steps:

Priming with Silicone Metal Primer


  1. Pour your primer onto a clean applicator. Never place the applicator into the primer container.
  2. Apply a thin film of Silicone Metal Primer using a clean lint-free cloth. DO NOT use a brush for application. 
  3. Excessive application may result in a white powdery deposit, which must be removed before sealant application. This white deposit can be removed with a clean cloth dampened with the recommended cleaner. Reapply a fresh, lighter application of primer. A light application on a non-porous surface may best be accomplished by application with a clean, non-treated cloth or tissue dampened with primer.
  4. Allow the primer to dry for a minimum of 15 minutes before sealant application. Protection of the primed area from contaminants is essential to ensure proper adhesion.

Caution:

  • Primers are NOT to be substituted for good surface preparation. The substrate to receive the primer shall be thoroughly cleaned using the recommended cleaner, and dried, prior to the installation of the primer.
  • All cleaners or primers to be used on the structural glazing application should be poured from the original container into small containers and poured from this vessel onto the cleaning cloth to prevent contamination of dirt into the container.
  • Pour off only enough primer required for immediate use.



Step #3: Masking

Masking with tape


To ensure a neat sealant sight line, masking tape is commonly used to outline the joint to be sealed. This reduces sealant smears, which are often found aesthetically unacceptable.

  1. When masking is required, the tape must be immediately removed after the tooling has taken place and before the cure of the sealant begins.


Step #4: Sealant Application

After joint is verified to be clean, dry, and free of contaminants, primer has been applied (if necessary), and the backing material has been properly installed, the application of silicone sealant may begin.

Sealant application, gunning the product


  1. The surfaces to which the silicone sealant will adhere should be designed smooth: free of nubs, serrations, grooves, or other features, so as to not impede the flow of the silicone sealant or wetting of the sealant to the substrates on its entire surface contact depth.
  2. Compatible structural spacers shall be installed to keep the glass properly spaced as per the approved drawings. Face clearance created by the structural spacer should be a minimum of 6.35mm (1/4”) wide to accommodate penetration of the sealant to the full depth of the cavity.
  3. Prime surfaces while taking care to protect the surfaces that do not require primer. If primer is applied accidentally on surfaces other than the one specified, it should be removed immediately with the help of a clean cloth dampened with the recommended cleaner.
  4. When gunning the silicone sealant into the cavity created by the structural spacer between the glass and the metal, a back pressure should be created such that the silicone sealant swells up behind the nozzle tip above the sight line, promoting full depth penetration of the sealant. Air pockets or voids along the edges are not acceptable and should be reported to the job foreman for immediate repairs.

Tooling the sealant


  1. All sealant beads must be tooled immediately after application, forcing the sealant into contact with the sides of the joint, promoting a full and continuous contact of the sealant with both substrates. This reduces the risk of air entrapment within the tensile bead. Avoid pulling the sealant out of the joint by frequent cleaning of the tooling instrument. Dry tooling is the recommended tooling method. Do not tool with soap, solvents, or detergent solutions.
  2. Areas that have been smeared or otherwise contaminated with unwanted silicone sealant should be cleaned before the sealant has an opportunity to cure. This is best accomplished with an IPA solvent-soaked cloth followed by a dry rag wipe. Failure to do so immediately can lead to very costly removal methods later on.

Caution:

  • Use structural silicone sealants within their stated shelf life. Verify the batch numbers and expiration dates of both the curative and base components of the silicone sealant upon receipt. Store in a dry environment, temperature between 15 to 27 °C (60 to 80 °F).



Glazing and Façades Specialist

Tremco CPG makes the process of selecting and installing the right glazing system simple and efficient. We offer a variety of tested, proven transition solutions that can accommodate any design, from standardised to highly specialised. All our weatherproofing products provide the highest performance in adhesion, weatherability and durability to guarantee a safe and leak-free building. Our expert team are on hand to help you in any current or upcoming project you may have, do get in touch with the team.

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