Drywall mud comes in two separate forms; pre-mixed or dry. In both forms water needs to be added to increase the workability of the material, and the amount of water can be changed depending upon what the mud will be used for. When working with drywall mud there are two main considerations: the rated dry time for the material and its workability.
Dry time is an important feature for drywall mud because the longer the dry time is the longer a person has to wait before they can do anything else to the surface where the mud was appplied. In dry mud there are a total of five different dry time ratings: 5 minute, 20 minute, 45 minutes, 90 minutes, and 210 minutes. However, it is important to remember that the dry time rating is a rating developed when the conditions are optimal for drying: a dry room at normal room temperature and plenty of air circulation. If a room varies from those conditions the dry time can vary as well.
The "workability" of the drywall mud is a very broad consideration but, like in any project, the easier the material is to work with the more efficiently the job can be completed. For example, when dealing with workability in drywall mud the main things that a "Drywall Finisher" are concerned about are: how much will the mud have to be mixed before it can be worked with, how many coats will have to be applied to the wall, and how much will the material have to be sanded. When a material is easier to work with it allows for a better finished product in a shorter amount of time.