a reactive alumina able of forming hydrated phases in water has been used as an alternative hydraulic binder in refractory castables. however, it has been observed that the drying of these materials is usually slower comparing to cement containing compositions. due to reduction of the permeability, this aspect increases the difficult of the vapor migration and can promote water vapor pressurization inside the structure and, eventually, explosion of refractories. additives usually used in refractory castables, in order to promote matrix dispersion, are shown to affect the hydratable alumina hydration mechanism. the dispersion of binder particles presents a main role in the development of hydratable phases but the coating of the particles surfaces by the additive inhibits the hydration. comb-like chain additives were indicated in order to match dispersion and hydration of castables containing hydratable alumina as a binder.