The synthesis of crystalline layered sodium silicates from amorphous sodium silicate has been investigated. Different synthesis process variables have been studied to synthesize products of a suitable quality for their use as builders in detergent formulations. Two different experimental processes have been used: a furnace (discontinuous process) and a pilot-plant rotary tubular oven (continuous process). The capacity to remove calcium and magnesium ions from water directly depends on the crystallinity and the delta phase content of the samples. The presence of about 20 wt % crystalline seeds and a reaction temperature of around 685 degrees C are needed to synthesize highly crystalline delta layered silicates. Differential thermal analysis measurements confirmed that amorphous silicate undergoes a crystallization process (exothermic step at 685 degrees C) which is attributed to the formation of the crystalline delta phase. The increase in the crystallization rate produced by agitation in the rotary tubular oven resulted in shorter reaction times than those for the furnace experiments. Scanning electron microscopic analysis was performed for samples obtained at different reaction times in order to establish a possible crystallization mechanism.