The strength of concrete depends on the amount and period of hydration. The process of keeping it hydrated for a long time while it hardens is called curing.
Therefore, a curing agent in context of tile flooring is nothing but a chemical used for finishing a newly created concrete floor. This agent is sprayed while a concrete structure is in the process of construction. It is sprayed on the surface to regulate the speed at which concrete would dry up.
If concrete dries out fast, it will end up being weak. It happens because the chemical bonding responsible for making the concrete sturdy does not get adequate time to complete its formation.
Spraying this agent on the floor can sometimes make the adhesive weak, which is responsible for securing tiles. This is because chemical used for slowing the process of curing can interfere with chemical bond created by tile adhesives.
That is why many people advice not tiling directly on a concrete floor that has just been cured using these agents. A level agent should be used first which is used primarily for making concrete slab levels. However, one can also use it as a primer that allows the adhesive to bond properly with floor surface.