ZnPO4 setting time is 4-7 min. All of the following methods are employed to prolong its setting time except:

Control of setting time​: ​Manufacturing process​ Sintering temperature : The higher the ​temperature, the more slowly the cement sets.​ Particle size : Finer particles react more quickly as a greater surface area is exposed to ​the liquid.​ Water content of liquid : Presence of excess water accelerates, whereas insufficient water ​retards the reaction.​ Buffering agents : When added, slow down the reaction.​ ​Factors under control of operator​ Temperature : Higher temperature accelerates the reaction. Cooling the mixing slab is an effective way of slowing the reaction and prolonging the working time.​ Powder-liquid ratio : More the liquid, slower the reaction. ​ Rate of addition of powder to liquid : The reaction is slower, if the powder is incorporated slowly.​ Mixing time : The longer the mixing time (within practical limits), the slower is the rate of reaction. Ref: Manappalil P: 90​