What do you know about silicone sealant?

Silicone adhesives (often referred to simply as "silicone") are a type of organosilicon product. They are primarily categorized by the byproduct released during curing: acetic acid-releasing, alcohol-releasing, amine-releasing, and oxime-releasing types. "Glass glue" is the common term for silicone adhesive; this name arose because consumers primarily use silicone sealants for bonding and sealing glass applications. Chemically, silicones are polymers composed of polydimethylsiloxane and silicon dioxide. Silicone adhesive is an ointment-like material that cures into a tough, rubber-like solid upon contact with moisture in the air.

I. Classification of Silicone Adhesives

Single-component and two-component.
Single-component silicone adhesives cure through a physical change triggered by contact with atmospheric moisture;
Two-component adhesives consist of two separate parts (Part A and Part B). Neither part can cure on its own, but curing occurs once the two components are mixed together.

Single-component silicone glass glue is the most common type on the market. Based on their properties, single-component silicone glass glues are further divided into acidic and neutral types. Acidic glass glue is primarily used for general bonding between glass and other construction materials. Neutral glue overcomes the drawbacks of acidic glue—specifically its tendency to corrode metal and react with alkaline materials—making it suitable for a wider range of applications; consequently, it is slightly more expensive than acidic glue. A specialized category of glass glue found on the market is silicone structural sealant. Because it is used for the structural or non-structural bonding and assembly of metal and glass components in glass curtain walls, it represents the highest grade and quality standard among glass glues and commands the highest market price.
1. Primarily used for the structural or non-structural bonding and assembly of metal and glass components in glass curtain walls.
2. It can directly bond glass to metal component surfaces to form a single assembly unit, meeting the design requirements for fully concealed or semi-concealed frame curtain walls.
3. Structural bonding and sealing of insulating glass units.

II. Use of Silicone Sealant

1. Application: Single-component silicone glazing sealant is ready for immediate use; it can be easily dispensed from the cartridge using a caulking gun, and the surface can be smoothed with a spatula or a piece of wood.
2. Skinning Time: The curing process of silicone sealant proceeds from the surface inward. Skinning and curing times vary depending on the specific properties of the sealant (please contact an XMC sales representative or refer to the Technical Data Sheet—TDS—for detailed specifications). Therefore, any surface tooling or smoothing must be performed before the sealant skins over (typically within 5–10 minutes for acidic and neutral clear sealants, and within 30 minutes for neutral colored sealants). If masking tape is used to cover an area, it must be removed after application but before the sealant skin forms.
3.  Curing Time: The curing time increases with the thickness of the sealant application. For example, a 12mm-thick layer of acidic sealant may take 3–4 days to fully cure, although a 3mm outer layer will cure within approximately 24 hours. When bonding glass, metal, or most types of wood, the bond achieves a peel strength of 20 pounds per inch after 72 hours at room temperature. If the application area is partially or fully enclosed, the curing time depends on the degree of confinement; in a completely airtight space, the sealant may never cure. Elevated temperatures will cause the sealant to soften. The gap between metal bonding surfaces should not exceed 25mm. In all bonding applications—including enclosed spaces—the bond quality should be thoroughly inspected before the assembled unit is put into service. During the curing process, acidic sealant releases an odor due to the evaporation of acetic acid; this odor dissipates during curing, leaving no residual smell once fully cured.
4.  Bonding:
A. Thoroughly clean metal and plastic surfaces to remove oil and grease. For plastic surfaces, rinse the entire area with acetone first; for rubber surfaces, abrade with sandpaper and then wipe with acetone. Observe all safety precautions when using acetone. 
B. Apply the silicone sealant evenly onto the prepared surface. If bonding two surfaces, position one side first, then press the other side firmly against it to expel air, taking care not to squeeze out the sealant itself.
C. Allow the bonded assembly to sit at room temperature until the sealant cures.
5. Sealing: When using silicone sealant for sealing applications, follow the same steps as above; firmly press the sealant into the joint or gap to ensure full contact with the surfaces.
6. Cleaning: Uncured sealant can be wiped off with a cloth or paper towel; once cured, it must be scraped off or removed by scrubbing with solvents such as xylene or acetone.
III. Application Areas for Different Silicone Sealants

Acid-Cure Silicone Sealant
1. Suitable for sealing, leak-proofing, and weatherproofing applications; effective for both indoor and outdoor use (with superior results indoors), offering excellent resistance to seepage and leaks.
2. Bonding various automotive interior components, including metal, fabrics, synthetic textiles, and plastics.
3. Bonding gaskets for heating and cooling equipment.
4. Attaching non-threaded stiffeners, nameplates, and painted plastic components to metal surfaces.
5. Sealing oven door windows, gas appliance flues, pipe joints, and access doors.
6. Forming in-place leak-proof gaskets for gearboxes, compressors, and pumps.
7. Sealing marine cabins and windows.
8. Sealing windows for trailers and truck cabs.
9. Bonding and sealing equipment components.
10. Forming anti-abrasion coatings.
11. Sealing and filling gaps in sheet metal laminates, ductwork, and equipment housings.
Neutral Weather-Resistant Silicone Sealant
1. Suitable for weather-resistant sealing of various curtain walls; highly recommended for glass curtain walls, aluminum-plastic composite panel curtain walls, and dry-hung stone facades.
2. Sealing joints between materials such as metal, glass, aluminum, ceramic tile, acrylic (Plexiglass), and coated glass.
3. Sealing joints on surfaces including concrete, cement, masonry, stone, marble, steel, wood, anodized aluminum, and painted aluminum. In most cases, no primer is required.
Silicone Structural Sealant
1. Primarily used for the structural or non-structural bonding and assembly of metal and glass in glass curtain walls;
2. Capable of directly bonding glass to metal component surfaces to form a single assembly unit, meeting the design requirements for fully concealed or semi-concealed frame curtain walls;
3. Structural bonding and sealing of insulating glass units.

IV. Development Trends of Silicone Sealants
Silicone structural sealant is a high-end bonding and sealing material based on hydroxyl-terminated siloxane polymers and multifunctional siloxane cross-linkers, prepared through processes such as compounding, mixing, and homogenization. It cures at room temperature (RTV) and offers elastic bonding capabilities, along with excellent mechanical properties across a wide temperature range and superior aging resistance. Available in single-component packaging, it features rapid curing, ease of use, and storage stability, playing a pivotal role in markets such as architectural waterproofing, doors, windows, curtain wall structural glass assembly, and architectural decoration. With technological breakthroughs in domestic silicone sealant products and the localization of production equipment, the number of manufacturers has risen steadily over the past decade. While product varieties and output have grown rapidly, market competition has intensified, showing a trend toward price-based competition that erodes profit margins year by year. This is particularly evident when raw material monomer supplies face sudden shortages and price surges; some manufacturers, unable to withstand the dual pressure from upstream and downstream sectors, are forced to exit the market. Conversely, robust enterprises that prioritize technological innovation can turn these adverse factors into opportunities, expanding their market share through high-quality, premium-priced offerings and innovative functional products. As a major developing nation, my country is experiencing sustained growth in building construction—particularly in curtain walls—driving a continuous rise in the total demand for architectural sealants. In this expanding market, competing solely on low prices is merely a short-term strategy; long-term, stable development within the construction market relies on a commitment to quality and technological innovation.