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What does ‘Setting Time’ and ‘Period of Plasticity’ mean?

period of plasticitySetting Time

The setting time generally means the elapsed time from the moment that the gypsum plaster is added to the water until the mix becomes hard enough to handle as a solid mass. During the first portion of the setting time, the plaster is very fluid and can be poured; a little later, it is in a plastic state during which it can be worked with templates and tools.

 

Period of Plasticity

This later stage in the thickening of the mix is called the "period of plasticity", and its duration varies according to the particular type of gypsum plaster being used. This period is one of the most valuable properties to be recognized in a particular plaster, for it is during this period that the gypsum cement can be manipulated to build up models over a framework or can be turned in a box or on the wheel. The evaluation of how a particular material handles during this period can best be learned by mixing actual test batches, following the guide-lines for mixing given in the manufacturer’s technical data sheets for the particular material. Important as the period of plasticity is, however, most of the methods described here involve using plaster even earlier in its setting time, when it is still liquid and easy to pour. Setting time and the period of plasticity are both influenced by the amount of water used to mix the given amount of plaster - the water-to-plaster ratio.