The correct water content is one of the major factors that influence the quality of refractory castables. Excess water can reduce strength and density, Increase volume shrinkage, and promote segregation of the castable ingredients. Insufficient water can produce “honeycombs” (air voids) in castable because of poor consolidation during placement, and prevent complete hydration of cement
The flow test is subjective and somewhat depends on the skill of the operator. It is a universally accessible method for determining how much water should be added to a vibracast refractory.
Place a convenient amount of dry castable into whatever device ( mortor box, concrete paddle mixer or Hobart mixer) you will be using. Begin mixing while adding water until the material appears moist, lumpy and, shiny. Form a hand-sized compact ball of the material on a vibrating table or in the form where it can be vibrated. The ball should flow to a pancake appearance after about 9 to 18 seconds. When this consistency is achieved, the castable is ready to be vibrated into place. The amount of water required should be reported in percent by the following calculation:
Ibs H2O/Ibs dry castable x 100