The seals or sealants are products that are used to seal gaps between two movable parts, especially in an automobile or block the passage of fluids through surfaces, joints or openings. Both the terms are used interchangeably. Seals/sealants can be weak, strong, flexible, rigid, temporary or permanent. Seals can also be classified according to their use, like industrial, construction, mechanical or home use.
The differentiation that you need to make at this juncture is between adhesive and seal. Sealants have lower strength but higher elongation because they are used between two substrates of different materials, having different coefficients of expansion. Hence, sealants need to be flexible, wellendichtring and expandable. On the other hand, adhesives are used to stick two different materials, as in glue. Most sealants are made of an inert material, so that they do not interact with other materials, and often made of an elastic material to fill the gaps between different surfaces.
Different types
Standard Seals
Standard seals include those for filling gaps between household materials, as in a washer used in faucets or 
plumbing pipes. These bushings are made of rubber, and hence, are also known as rubber sealants.
Paints and varnishes are also standard seals that are used not only for aesthetic purposes but also to prevent rusting of metal surfaces or prevent water from seeping into buildings.
Special Seals
The Special seals include those used in various industrial applications, as in industrial pipes for the flow of gases, liquids and other chemicals that are produced or used in different factories and industries. Similarly, industrial seals can be used in various automobile applications that are used in automobile engines, gasoline pipes, etc.
Another form of industrial seals can be in the transmission of water from water treatment plants to various homes. Two tubes of the same size are sealed with a layer of sealant between the pipes and fixed using nuts and bolts. Some standard sealants are also used for dental applications, as in providing an enamel cap or using sealants to attach teeth to a base.
Application
The final application of industrial seals is in the field of construction. Cement is a material that hardens when water is mixed with it. Additionally, cement, when mixed with materials like fine aggregate, coarse aggregate, and water, becomes concrete. Concrete inherently has problems because it does not dry uniformly. To save concrete from having pores, construction seals, like putty, silicone, paints, etc. are applied so that the pores are closed.
As you can see, there are a wide variety of applications for sealants. Some sealants have standard applications, as in homes, and plumbing appliances. Other sealants have specialized applications, as in automobiles, water transmission pipes, in manufacturing set-ups, and other applications.…