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
The P/L  ratio  can  be  reduced  to produce a thinner mixture
Smaller portions of powder should be mixed for the first few increments
Colder mixing temperature (though temperature of mixing slab should be above dew point)
All of the above