What Is the Difference Between Adhesive and Sealant?

Adhesives and sealants are two different products with very different applications. Sealants are used to fill gaps and resist relative movement while adhesives are used to bind surfaces together.

Both offer benefits, but they should be selected based on the substrates, anticipated movement, and environmental conditions. It is also important to review product data sheets and literature carefully.

Sealants

Sealants are used to fill gaps and cracks to prevent air, water or other substances from passing through. They are typically more flexible than adhesives, allowing them to withstand movement without cracking or breaking. Sealants may be made from a wide range of materials such as silicone, polyurethane or butyl.

Unlike adhesives, which are designed to bond surfaces together, sealants are intended to grip substrates at the molecular level and create a barrier that cannot be penetrated. This makes them a more versatile material that is ideal for use in a number of different applications and environments.

Important mechanical properties of sealants include elongation, compressibility, tensile strength and modulus of elasticity. These properties are important because sealants must be able to move and change shape with changes in temperature and other environmental conditions without losing adhesion or failing.

The elongation and flexibility of a sealant are determined by its viscosity, which can be modified through the addition of fillers and other ingredients. It is also possible to adjust the elasticity of a sealant by selecting the appropriate polymer for its formulation.

A sealant must be able to resist deformation under stress in order to withstand the cyclic movements of a joint. This property is determined by testing the tensile adhesion properties of the sealant using equipment that simulates several cycles including water immersion, artificial weathering (sun exposure and water spray at various temperatures) and drying.

Adhesives

Adhesives are substances that help stick two different materials together. They’re used in a variety of ways, from sticking envelopes to repairing furniture and many other applications. Modern adhesives are manufactured by a wide range of processes, both natural and synthetic. Some are even very strong and durable.

There are three different types of adhesive: structural, contact and pressure-sensitive. Structural adhesives are offered in paste, liquid or film adhesive & sealant forms and can be very strong. They are typically used below their glass transition temperature (Tg), which is the point where polymer molecules begin to deform into a soft rubbery material. This class of adhesive includes epoxies, cyanoacrylates and urethanes.

Contact adhesives wet the surfaces they’re bonding, displacing all air and allowing them to adhere very closely. This type of adhesive is often used for food packaging and paper wrapping. Pressure-sensitive adhesives do not harden at all, instead remaining permanently sticky.

Depending on the chemistry of an adhesive, it can form bonds by physical adsorption, electrostatic attraction or chemical bonding. Natural adhesives are derived from animal or vegetable oils and have long dominated the industry. However, they are less popular now than synthetic adhesives that use raw materials from renewable sources. The chemistry of an adhesive can also affect its load bearing capacity, which is important for many projects.

Substrate Preparation

Substrate preparation is the set of activities, codes and standards that must be performed to prepare a material’s surface before it receives a protective coating. This preparation may include chemical cleaning, shot blasting or sand basting, and acid etching. All these methods are designed to prepare a material’s surface so that the bonding process can be effective and efficient.

Proper substrate preparation is a critical element in many applications, especially when the adhesive or sealant will be exposed to environmental conditions. This is because many of these conditions cause damage to the adhesion bond if the material’s surface is dirty, oily or otherwise compromised.

For instance, humidity can trigger corrosion failure in some materials, because invisible contaminants (such as chlorides) attract moisture through the substrate, causing it to degrade the adhesive or sealant bond. Other factors that affect adhesion include drying, the adhesive chemistry, coat weight and curing.

For example, a concrete substrate needs to be cleaned and smoothed before sealant application. A simple two-cloth method is a good way to do this, using solvent on the first cloth and then a dry cloth. If the concrete is rough, diamond grinding might be used to correct irregularities and ensure a clean, smooth substrate for sealant performance. This preparation is also critical for adhesive & sealant bulk substrates such as straw. A quick and organic way to prepare straw for mushroom cultivation is by pasteurizing or sterilizing the substrate in a glass jar, and then adding vermiculite and brown rice flour.

Application

A wide range of materials are used to bond and seal items in industrial applications. These include adhesives, caulks, sealants, and glues. While these materials are similar on a basic level, they differ in application and function. They also offer varying levels of durability, strength, flexibility, and ease of use. Choosing the right type of adhesive or sealant is important for an efficient assembly process.

Engineers need to consider factors such as the substrates that are being bonded, the working and curing conditions of the material, and environmental influences. Proper storage and handling is also critical for ensuring that the adhesive or sealant remains effective.

Adhesives offer a strong bond that reduces the need for mechanical fasteners and saves time in assembly. They also distribute stress evenly across the bond line to increase durability. In addition, they can be applied in a continuous line or pattern, reducing overall assembly time and cutting down on material waste.

There are a variety of different adhesives on the market, including epoxy, epoxy resin, and acrylics. Epoxy adhesives are designed for structural attachment and provide high adhesive force and resistance to chemicals. They come in sprays, emulsions, and other liquid forms and are compatible with a range of materials. Acrylics are easy to apply and provide a high-strength bond for light-duty projects. They are also resistant to water and weathering.