Tiles are soaked in water for various purposes, some are listed below;
1. During manufacturing, the oil is used. to remove that oil film from the tile back surface, tiles were soaked in the water. As the oil is having low density than water, all oil coating comes out of the tile and floats on the surface of water (this is very old practice and now a days oil is not used by manufacturers).
2. As rightly said by
@Mula Akhil, Ceramic tiles has high water absorption rates, if tiles used without pre-soaking, it will absorb the water from cement paste or adhesive which lead to less water for hydration / curing and the weakening of bonding between tile and binder.
3. During the transportation of the tiles from factory to site location or during shifting from site to site or store to work place, there are chances of tile getting damaged. Those damages generally occurs in back clay of tile as the glaze is harder. Such cracking or damage is not visible and may come on surface of glaze after installation and during curing period.
In order to ensure there are no defects or damages in the tile, it is recommend to soak it in water for at least 2 hours before installation. when tiles are soaked and has any defect in it, during taking out of tile from water, tiles get break at location of cracks and indicates that tile is defective. If percentage of such tiles is observed more, the action can be taken immediately by calling to manufacturer for replacement of lot.
Now a days, a powdery non sticky agents are used during tile manufacturing process, when tiles come out of the heating area, it is coated with powder which protects the tile surface from getting any kind of stains. When doing tiling work we should also ensure that, the back surface of tile is wiped with wet rag / cotton piece to remove that powder coating stuck on back surface of the tile.
So irrespective of type of tile, we should do soaking for minimum 2 hours in water and during installation we should wipe the back surface of tile with wet rag.