The invention concerns a method for producing a hardened mineral product, especially concrete. The method utilizes a hydration reaction with water for at least 1 hour, preferably for 4 to 40 hours, by producing a water/binding agent paste containing components for retardation of binding agent crystallization together with other possible admixtures, e.g., accelerators. When the binding agent reaches an appropriate degree of hydration, preferably 10 to 90%, the unset paste is complemented with fillers for producing the desired mineral mix, after which the end product is shaped as desired and hardened. The water/binding agent paste is agitaged in order to promote the hydration reaction, and when required, admixed with an additional amount of the retarding component of the binding agent crystallization. Furthermore, the invention includes an apparatus for hydrating the binding agent with a facility for subjecting the paste to compacting pressurization in order to improve hydration.