To be satisfactory, the sealant should possess the following desirable properties:
1. Impermeability: It must be an impermeable material;
2. Extensibility without fracture: As the joint opens and close the sealant must deform to accommodate the movement without losing its integrity. it should have good rupture strength (that is, not fail in cohesion). How lack of cohesion can break the sealer in winter when slab edges move apart.
3. Durability: It must be very durable as periodic renewal may be difficult and expensive. Ideally, the life should be the same as the structure of which it forms a part. This condition is, however, not fulfilled by any known sealant.
4. Adhesion: it must bond to the sides of the groove in which it is inserted and should not fail in adhesion. In practical terms this means that the sealant should bond well to the damp concrete. It should resist flow due to gravity (vertical joint in walls)
5. Non-Toxic: In potable water tanks the materials must be non-toxic and non-training and should not support the growth of bacteria and fungi.
6. Hardness at lower temperature: It should be comparatively easy to install under the weather and the site conditions relevant to the location of the structure. It should not harden and become unacceptably brittle at lower service temperatures.
7. Softening at higher temperature: Sealant should not unacceptably soften in hot weather and should also resist flow due to gravity (vertical joints in walls). In other words, the compound should not flow in hot season and become brittle in cold season. An unduly softening of compound in summer or hot weather would lead to spreading of the compound out of the joint leading to poor serviceability as shown in the following fig.
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