In this article we explain the key differences between adhesives and sealants, through an exploration of what makes up an adhesive and a sealant.
Overview of Adhesives
Adhesives are substances that are capable of bonding two or more separate substrates together by chemically overcoming the forces required to separate them. They are used in virtually every product that is composed of two or more parts, as they are often more efficient and easier to apply than mechanical fasteners. For more information regarding how adhesives provide advantages over mechanical fasteners, read our article “What Are Structural Adhesives?“.
Overview of Sealants
Sealants are flexible, paste-like substances that block the flow of fluids through a surface, gap or joint by filling all the spaces between two separate substrates. They have traditionally been used for waterproofing processes, although they also have applications in fire-retardants and thermal insulation. Whilst sealants are not the same as adhesives, some do possess adhesives properties. Similarly, many adhesives technologies can be formulated into sealants.
Key Differences Between Adhesives and Sealants
Although adhesives and sealants are often discussed under the same category of material, they do have crucial differences which make them fit for different purposes. A few of these differences are explained below:
- Adhesives have higher shear strength and lower elongation at break than sealants. Adhesives, generally, have over 1000 psi lap shear strength while sealants have less than 1000 psi. This is a result of adhesives having a greater cohesiveness, which means that their molecules stick together with much greater attraction.
- Adhesives are more rigid and durable than sealants.
- Sealants don’t usually provide enough bonding force to hold two substrates together as a result of their less cross-linked molecular structure. Consequently, adhesives are primarily used for bonding due to their higher bond strength.
- Sealants are subject to creep (deformation) under a load.
- Sealants are more flexible than adhesives.
- Sealants usually contain an elastomer, which gives them a paste-like consistency.
- Sealants have higher rates of shrinkage and, therefore, are more effective at filling small gaps between surfaces and components. This is an effective means of making a space air and water tight.
- Pressure-sensitive adhesives aren’t ideal for gap-filling and encapsulating as they remain viscous and don’t fully solidify.
Considerations for Choosing Between Adhesives and Sealants
There are various factors to consider before deciding whether to use an adhesive or a sealant. These factors can be thought of as questions, such as:
- Are you performing a bonding operation? Does the bond have to support a load-bearing object? If so, you should use a structural adhesive.
- Are you looking to fill a gap between two or more substrates? If so, you should use a sealant.
- Are you looking to keep moisture in or out of a component? If so, you should use a sealant. In addition to making components watertight, this sealing property of sealants can also be used for thermal and acoustical insulation, fire-retardants and electrical conductivity.