Sealants are used in construction to prevent fluids and other substances from passing through material surfaces, joints, or openings. They can also prevent the passage of air, sound, dust, insects and so on, as well as acting as a firestopping component.
Sealants are typically used to close openings between that are too small for other materials such as concrete, timber or mortar to be used. They have a wide range of properties in terms of strength, flexibility, appearance permanence, solubility, corrosion resistance and so on.
While some selants have adhesive qualities, they differ from conventioanl adhesives in that they tend to have lower strength and higher elongation. This means that they can be used more flexibly between substrates with different properties.
Historically, materials such as plant resins, mud, grass and reeds were used as sealants. Glazing putty was first used in the 17th century as a means of sealing window glass into the panes. Sealants were first chemically manufactured in the 1920s, in the form of acrylic, butyl and silicone polymers. Synthetic-polymer-based sealants became widely available for use in construction by the 1960s.
The three basic functions of a sealant are as follows:
- Fill a gap between two or more substrates.
- Form a barrier through which other substances cannot pass.
- Maintain sealing properties for the anticipated lifetime.
These functions can be achieved by matching the most suitable sealant to the substrate materials, i.e. one that will have adequate bonding properties and be flexible enough to tolerate anticipated movement, and so on.
Sealants may have a high viscosity, meaning that they do not flow from where they are applied, or a low viscosity, allowing them to penetrate into a substrate. Anaerobic acrylic sealants are able to cure in the absence of air, whereas surface sealants require air to cure.
Some of the most common types of sealants include:
- Acrylic resins
- Butyl rubber
- Epoxy thermosets
- Expanding foam
- Hot wax
- Latex sealants
- Metal sealants
- Paint sealants
- Polysulfide sealants
- Polyurethane sealants
- Rubber sealants
- Silicone sealant
- Urethane sealants
Sealants are typically applied using a caulk gun with a plunger mechanism. Some of the variations include:
- Stamped-steel caulk gun: The least expensive type, which can be disposed of after use.
- Manual caulk gun: Heavy duty for moderate construction use. Has a strong steel body and cast iron handle.
- Bulk caulk gun: This is used for fast application and is designed to accept sealant supplied in bulk.
- Air-powered caulk gun: Capable of pumping high viscosity sealants at high speed and in large volumes.
In certain circumstances, soldering or welding can be used as alternatives to sealants, although these involve more complex techniques.
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