A sealant’s function is to form a protective barrier against water, air, or other elements from penetrating the materials and substrates they are applied on. Generally, a sealant does this by two simple principles – adhesion to the substrate, and cohesion of the sealant itself.
Adhesion means the chemical bond between the sealant and the substrate – in the case of a silicone sealant applied on a bathroom sink, the sealant is the silicone polymer, while the substrate is the ceramic sink and granite counter. By “sticking” to the substrates, the silicone ensures that water cannot penetrate through them. Without a sealant, water would easily pass into the crack between sink and counter.
Cohesion means the chemical bond within the sealant itself. Sealants require substantial volumes to work in the sense that they need to have a bead (in contrast to adhesives which only requires a minimal layer). The integrity of the sealant, therefore, is important to prevent water from getting through. If a sealant cracks, it will allow water seepage. If a sealant is easily dissolved, it will also allow water seepage once it has disintegrated.
To make things clearer, we’ve prepared this sealant infographic for your reference.