What is the application process for silicone sealant?

What is the application process for silicone sealant?
The application process for silicone sealant directly impacts the final bond strength, sealing, and durability. It requires strict adherence to the four core steps of “substrate pretreatment → sealant preparation → sealant application → curing and curing.” Particular attention should be paid to substrate compatibility (e.g., avoiding contact between acidic sealants and PVC/WPC), controlling the thickness of the sealant layer, and ensuring a suitable curing environment. The following is a detailed process and key technical points:
I. Pre-application Preparation: Three Core Prerequisites (Determining Success or Failure)
1. Confirming Substrate Compatibility (Avoiding Corrosion/Adhesion Failure)
Preferably, neutral silicone sealants are suitable for most substrates, including WPC, PVC, metals (aluminum alloy, stainless steel), glass, and ceramic tiles. They are non-corrosive. Misuse of acidic silicone sealants can cause swelling and whitening of PVC and corrosion of the wood fiber layer of WPC. Therefore, they should only be used on inorganic substrates such as glass and ceramic. Small Area Test: When using a brand of silicone adhesive for the first time, apply a 1-2 cm strip of adhesive to a hidden area of ​​the substrate. After curing for 24 hours, inspect the following: ① Is there any discoloration or bubbling on the substrate surface? ② Is there clear adhesion when peeling the strip (no “peeling off” phenomenon?). Only apply to a larger area if the test passes.
2. Tool and Material Preparation
II. Formal Application: 4-Step Standard Process (with Key Techniques)
Step 1: Substrate Pretreatment (Critical for Adhesion)
Cleaning: Wipe the substrate surface on both sides of the gap (≥ 5 cm wide) with a lint-free cloth dampened with alcohol, focusing on removing oil, mold release agent (WPC/PVC boards may have a factory surface), and dust. Allow to dry for at least 10 minutes to ensure no alcohol residue remains.
Sanding (Optional but Recommended): If the substrate surface is smooth (such as PVC boards or mirror-finished metal), lightly sand with 120-grit sandpaper to create a slightly rough surface (to increase the adhesive contact area). Clean again with alcohol after sanding to remove sanding dust. Applying Masking Tape: Apply masking tape to the substrate on both sides of the gap, leaving the edge of the tape 1-2mm from the edge of the gap (ensure the tape can be easily removed after the adhesive strip cures, leaving a neat adhesive line). Ensure the tape is applied straight and avoid skewing.

Step 2: Hose Treatment (Ensure Even Extrusion of Adhesive)

Remove the plastic cap from the top of the silicone hose and use a utility knife to cut along the tapered guide line at the hose opening (the diameter of the hose opening = 1.2 times the gap width. For example, if the gap is 5mm wide, cut the hose opening to 6mm. Avoid using a tapered strip that is too thin and will result in an insufficient seal, or too thick and wasteful).

Attach the nozzle that comes with the glue gun and cut the nozzle tip at a 45° angle (the angle should align with the direction of application to ensure that the adhesive adheres to the gap). Then, install the hose into the gun and test the gun handle to ensure even extrusion without any breakage or clumping. (If there is any clumping, the adhesive is expired and needs to be replaced.) Step 3: Glue Application (Controlling Adhesive Layer Shape and Thickness)
Glue Application: Hold the glue gun at a 45° angle to the substrate, with the nozzle close to the bottom of the gap. Push the gun at a steady speed (approximately 5-10 cm/s) to ensure the gap is completely filled with adhesive (no bubbles or gaps). Keep the nozzle moving in the same direction as the gap.
Glue Layer Shape (Critical): A “triangular glue layer” (isosceles triangle cross-section, height = 1-1.5 times the gap width) is preferred. This provides a 30% larger bonding area than a “rectangular glue layer” and better accommodates thermal expansion and contraction of the substrate (avoiding cracking). If the gap depth is greater than 10 mm, first fill it with a foam strip (the distance from the top of the foam strip to the substrate surface equals the glue layer height) before applying glue. Glue Repair and Scraping: Within 10 minutes after applying the glue (before the glue has dried on the surface), use a rubber scraper to gently scrape the surface of the glue strip along the gap (holding the scraper at a 30° angle to the substrate). Remove any excess glue (which can be recycled back into the hose to avoid waste), ensuring a seamless bond between the adhesive layer and the substrate, with no bumps or indentations.
Step 4: Curing and Curing (determines the final performance of the adhesive layer).
Removing the Masking Tape: Within 30 minutes to 1 hour after scraping (before the glue has dried on the surface but not fully cured), quickly remove the masking tape perpendicular to the substrate to prevent it from sticking. (If it does stick, gently wipe it with an alcohol-soaked cloth; do not use a razor blade to avoid scratching the substrate.) Curing Environment Control:
① Temperature: Neutral silicone adhesive requires a curing temperature between 5°C and 35°C. Temperatures below 5°C will result in slow curing (possibly requiring over 72 hours), while temperatures above 40°C can cause bubbles to form within the adhesive layer, affecting sealing.
② Humidity: A relative humidity of 40% to 80% is optimal. Excessive dryness (<30%) will prolong the curing time. Excessive humidity (>90%) or rainy days require shelter to prevent rain from eroding the uncured adhesive layer.
③ Ventilation: Maintain good ventilation in the construction area to accelerate the evaporation of volatile components in the adhesive and prevent the adhesive layer from becoming sticky.
Full Curing Time: Surface dry time (non-sticky surface) is approximately 1-2 hours, initial curing (able to withstand light external forces) is approximately 24 hours, and full curing (achieving optimal bond strength and weather resistance) takes 7 days. (Single-component silicone adhesives cure by absorbing moisture from the air; the thicker the adhesive, the longer the curing time.) Avoid stress, impact, or contact with oil or dirt on the substrate before full curing. IV. Post-Application Inspection (Quality Assurance)
After complete curing (7 days), perform three key inspections:

Sealing Test: For outdoor or humid environments, spray the adhesive layer with water (water pressure 0.2MPa) for 5 minutes to check for water seepage from the inside of the gap. If no water seepage occurs, the seal is satisfactory.

Adhesion Strength Test: Gently pull the adhesive layer by hand. If there is a noticeable pull and no “easy peeling” phenomenon, the bond is satisfactory.

Appearance Inspection: The adhesive strip surface is smooth, free of cracks and bubbles, and the transition to the substrate is natural. There are no traces of masking tape left, indicating a satisfactory appearance.

Following the above process ensures that the silicone sealant achieves optimal bonding, sealing, and weather resistance, making it particularly suitable for critical applications such as outdoor WPC panels, PVC wall panels, and glass curtain walls.