In modern construction, ensuring the durability and integrity of structures is essential. One critical element in achieving this is the use of sealants, which play a vital role in protecting building components from environmental stress, moisture infiltration, and structural movement.
Introduction to Sealants
A sealant is a material used to seal joints or gaps between different building materials such as concrete, glass, aluminum, and masonry walls. These joints are intentionally designed into structures to accommodate thermal expansion, contraction, and other forms of movement that could otherwise lead to cracks and structural damage.
Sealants not only provide a barrier against water and air infiltration but also contribute to the longevity and performance of the structure by maintaining joint integrity under varying conditions.
Properties of a Good Sealant
For a sealant to be effective in construction applications, it must possess certain key properties:
- Strong adhesion to various building materials
- Softness and flexibility to accommodate movement
- Weather resistance to withstand exposure to sunlight, rain, and temperature changes
- Resistance to repeated stress cycles without degradation
These characteristics ensure that the sealant remains functional over time, even in dynamic environments.
Types of Sealants Used in Buildings
There are several types of sealants commonly used in the construction industry:
- Silicone-based sealants
- Urethane-based sealants
- Acrylic-based sealants
- Polysulphide-based sealants
Among these, Polysulphide-based sealants are widely preferred due to their excellent performance in both residential and commercial construction projects.
Polysulphide-Based Sealants
A. Overview
Polysulphide sealants are known for their superior elasticity, chemical resistance, and long-term durability. They are particularly suitable for use in cold weather conditions and are often chosen for applications where high flexibility and resistance to harsh environments are required.
B. Types of Polysulphide Sealant Systems
- Two-part system
- Composed of two components: a base and an accelerator.
- Must be mixed before application, after which a chemical reaction begins.
- The resulting paste has a working life of approximately 48 hours.
- Full curing typically takes about 8 days.
- Available in two forms:
- Gun grade: ideal for inclined, vertical, and overhead joints
- Pour grade: best suited for horizontal joints
- One-part system
- Pre-mixed and ready to apply directly from the container.
- Cures through absorption of atmospheric moisture.
- Full curing time ranges from 3 to 4 weeks.
- More convenient for small-scale or less technical applications.
Applications of Polysulphide-Based Sealants
Polysulphide sealants are versatile and find use in a wide range of construction applications, including:
- Building structures:
- Basements, glazing frames, ceiling joints, floors, roofs, external walls, cladding, retaining walls
- Water-retaining structures:
- Dams, reservoirs, canal linings, culverts
- Infrastructure projects:
- Joints in bridges, roads, and aerodromes
Their ability to perform under pressure and resist environmental factors makes them a top choice across multiple sectors.
Equipment for Applying Polysulphide Sealants
To ensure proper application and performance, the following tools and accessories are commonly used:
- Filling device: Ensures the sealant is protected from the atmosphere and allows for efficient dispensing, especially in large-scale jobs.
- Gun: Typically includes PVC cartridges and nozzles for precise placement in joints.
- Mixer: Required for two-part systems to ensure thorough blending of the base and accelerator.
- Spatula: Useful for smaller applications where a gun may not be necessary.
- Backup material: Helps control the depth of sealant within the joint.
- Bond breakers: Usually made of PVC, metal, or paper; they prevent three-face adhesion.
- Masking tape: Protects adjacent surfaces from unwanted sealant spread during application.
Working Conditions for Polysulphide Sealants
Several environmental and operational factors influence the performance and effectiveness of Polysulphide sealants:
- Temperature
- Application temperature: 5°C to 50°C
- Service temperature range: –40°C to +80°C
- Joint Size
- Recommended width: 5 mm to 50 mm
- Depth:
- 5 mm for metal and glass structures
- 10 mm for concrete and brick joints
- Storage
- Mixed two-part sealant should be stored in a cool, dry place in sealed containers for up to 12 months.
- Water and Chemical Resistance
- Fully cured Polysulphide sealants are impermeable to water.
- Highly resistant to oils, petrol, white spirit, and other fuels.
- Setting and Curing Time (varies with ambient temperature)
| Temperature (°C) | Setting Time (hours) | Curing Time |
|---|---|---|
| 5 | 72 | 8 weeks |
| 15 | 36 | 4 weeks |
| 25 | 18 | 2 weeks |
| 35 | 8 | 8 days |
- Movement Accommodation
- Can handle up to 25% movement in butt joints
- Up to 50% movement in lap joints
- Durability
- In high-traffic areas like roads and bridges, Polysulphide sealants can last up to 10 years
- In non-traffic applications, they offer service life of up to 25 years
Conclusion
Polysulphide-based sealants are among the most reliable and versatile options available for sealing joints in modern construction. Their exceptional flexibility, chemical resistance, and adaptability to extreme conditions make them ideal for a wide range of applications—from residential buildings to major infrastructure projects. By understanding their properties, application methods, and working conditions, professionals can ensure optimal performance and long-term durability of structures.