Provided herein is a composition for use as a hardening regulator, e.g. hardening accelerator or hardening retarder, for building materials, as well as methods for producing thereof. The composition is characterized by a biphasic nature in which solid calcium silicate nanoparticles are dispersed in an aqueous solution comprising inorganic water soluble iron, and possibly zinc, silicate and calcium, species. Additional components such as inorganic ions and silica nanoparticles can be present. Depending on the relative ratio of each component, the composition can be used either for retarding or for accelerating the hardening process of a building material such as cement or concretes. The so-obtained building material further shows an enhanced strength upon compressive forces applied thereon.