The usage of adhesives and sealants have ever been increasing in all the areas including manufacturing, Maintenance, construction, interior work et cetera.
Designers, architects, engineers, contractors, home users are experts in their respective fields. However, it becomes difficult to choose the right sealant for their applications. It is imperative that users are educated on how to choose the right sealant. This article attempts to do so.
Sealants are generally used to seal and bond STATIC joints / assemblies to protect against water ingress, weather, sunlight, heat et cetera. They also help in maintaining
structural integrity of the assembly with effective bonding.
Factors to consider during selection
- Gap between the joints in mm
- Flexibility of the joint depending upon if it is subjected to expansion/ contraction
- Exposure to external environment . Viz :
Sunlight – is it UV resistant
- Chemical resistance : exposure to corrosive chemicals, acids, fuels etc
- Temperature to be sustained by the assembly
- Expected life of the joint : sometimes sealant is used temporarily to hold parts together
- Paintability – can it painted over
- Ease of application
Classification of Sealants based on Technology/ Chemistry
1. Silicone Sealants
It is the most popular type of sealant used. The silicone variant checks all the boxes for the factors required when it comes to choosing a sealant. It is seen to be extensively used in manufacturing, maintenance, construction, interiors and in any sealing application.
Silicones are further classified based on their curing systems
Acetoxy - Cure Systems
- Most popular & used extensively due to lower costs.
- Disadvantages: not sensor safe, corrosive due to acetic acid vapours released during curing, cannot be painted over, strong smell.
- Applications: Gap-filling, high temperature (300°C) sealing, any general-purpose sealing/bonding application.
Neutral - Cure Systems
- Higher grade Silicone sealants used for technical and critical applications.
- Applications: Flange sealing in Automobiles, manufacturing, Plant maintenance, Food and Pharma plants for general bonding/sealing, External window gap sealing, Glass Bonding, glazing , weather sealing.
2. Polyurethane Sealants
- Characteristics: High gap filling, high bonding strength, flexibility , chemical resistance, weatherability, can be painted over.
- Construction: Expansion Joint sealing, internal joint sealing ( Eg: isolation joints)
- Windscreen Bonding: most popular application for PU sealants used in Automobiles, Railways.
- Automotive: for Bonding Panels in Bus body building, high vibration resistance, high bonding strength
- Manufacturing: general high strength flexible bonding
3. Acrylic Sealants
4. Hybrid MS Adhesives
- High bonding strength, instant bonding, low gap fill. Primarily used as a bonding agent than for sealing applications.
- Examples: Mirror Bonding, Panel Bonding, Cladding et cetera
5. Polysulphide Sealants
- It is the popular sealant used in expansion joints in Civil construction and concrete roads.
- They are of Two types : Gun grade and Pour Grade