Sealants, like adhesives, are designed for specific applications. The design criteria, production requirements, environmental conditions and economic costs must all be taken into account. Modern sealants are typically formulated from synthetic elastomeric polymers. They may contain fillers, plasticizers, thixotropic agents, adhesion promoters, catalysts and curing agents. They are also often supplied with external accessory materials such as primers, bond-breaker tapes and back-up materials.
Sealant manufacturers are found in numerous locations around the world. Most have multiple plants and are highly focused on quality and product development. Most are experienced in supplying their products to the construction, automotive and industrial markets. They know that the demands of these markets are incredibly diverse and that there is no single formulation that can be suitable across all applications.
The primary functions of sealants are to fill gaps, resist relative movement between substrates and exclude or contain another material. In some cases they are asked to perform several of these functions at once. They are generally lower in strength than adhesives, but they must still have sufficient flexibility to provide their desired performance.
In addition to providing the appropriate physical properties, sealants must be easy to handle and apply. A number of factors can impact these characteristics, including the type of application (single- or two-component systems, primer or non-primer systems), the surface to which they are being applied (dry or wet), the temperatures to which they will be exposed, and the ease with which they can be painted over or removed.
Another important criterion is the amount of load the sealant must hold in service. This will often require the sealant manufacturer to test their products in specific loading situations. It would be advantageous for a contractor or engineer to have access to this data and, if it is not available in the public domain, to request that the information be provided by the sealant manufacturer.
In many situations the sealant must also be able to withstand extreme temperature exposures. This is especially true in the case of applications such as sealing joints around hot water pipes. It is not uncommon for these temperatures to reach 70degC (158degF) or higher. A good manufacturer will be able to supply the data necessary for a client to assess if their products can endure these high temperatures.
Finally, the sealant manufacturers should be able to supply clients with information about chemical compatibility with a wide range of other construction materials. This is a vitally important criterion, and one which should be assessed through an industry test method such as AAMA/FGIA 713 Voluntary Test Method for Chemical Compatibility of Sealants and Self-Adhered Flexible Flashings. The test involves putting fresh sealant in contact with self-adhered materials and then evaluating them for discoloration, slump, degradation or liquefaction. This test method can help avoid the potential delays and cost overruns caused by poor chemical compatibility between a sealant and the materials with which it is being used.