Which of the following techniques can extend the working time of a zinc phosphate cement?
Control of Setting Time:
Manufacturing process

Sintering temperature: 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, slows down the reaction.

Factors under control of operator

Temperature: Higher temperatures accelerate 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: Longer the mixing time (within practical limits), the slower is the rate of reaction.

Ref: Manappalil P: 90