The setting reaction of zinc phosphate cement is exothermic. it needs to be mixed in increments and over a large surface area for dissipation of heat. Otherwise, with increase in temperature, the reaction will accelerate and the cement will set fast. the first increments are added to saturate the liquid and decrease the reaction speed, the next increments to get a uniform mix and final small increments to adjust the consistency of the mix as desirable for luting.
