There is movement in structures regardless of size, height, and width. To accommodate or cushion structural movement, there is need for elastic joints at varying strategic locations throughout the exterior of a building. In addition to the problem of potential torsion, seismic, or vibrational stresses, the dimension and location of joints are directly related to the tolerances and thermal movement characteristics of various substrates that make up the structure, potential shrinkage, and design esthetics.
The primary function of a joint sealant is to maintain a positive seal between the sides of a joint which may be subject to movement. It does not contribute in any way to the structural properties of the building; rather, it helps to control the environment within the structure by resisting the passage of heat, light, sound, rain, snow, wind, ordor, chemical and biological contaminants, and dust. At the same time, the sealant must withstand the effects of thermal, moisture, and structural movement, including vibration and creep. It also provides sound insulation. In some cased, the sealant will be required toperform other functions, such as withstanding attack by insects, microorganisms, plants, or pollution.
In order to perform all of the above functions, the sealant should possess these properties and features:
- Long term adhesion to the faces of the joint.
- Resistance to creep, slump or cold flow.
- Resistance to undue shrinkage.
- Non-bleeding or non-staining properties.
- Adequate elastic properties to accommodate movement without splitting.
- Resistance to specific chemicals.
- Compatibility with paint and protective coatings.
- Resistance to weathering and aging.
- Retention of physical properties.
- Stability in storage.
- Ease of mixing (if required).
- Ease of application
The life of a sealant may be extended by the nature of the joint, specifically a joint configuration where the sealant is protected by the structure (e.g. recessing the sealant within the joint so that its outer surface is shielded from the sun and weathering, or by appling sand; sanding the joint sealant).