Pumpable concrete starts with the aggregate. It is the combined gradation of the aggregates and their residual moisture absorption that are most important. A pumpable lightweight mix may differ from one that is not pumpable in having a higher plastic unit weight, especially if more natural sand is used. It may have a higher slump as it enters the pump and its dry unit weight at 56 days is greater by about two to five pounds per cubic foot. The next consideration is the volume of coarse aggregate that can be pumped. ACI 211.1-74, allow reduction of the coarse aggregate content by as much as 10 percent to provide more workable concrete, when required, for pumping. Nevertheless, if the gradation is poor it should first be improved. How much reduction should be made can be determined only by experience with the aggregates and with the particular pump being used. ACI 211.2 is not a recipe, but a "method for selecting and adjusting mix proportions" depending on the competence and available time of the mix designer and inspector, the trial mix of 211.2 can be improved in strength-related properties and economy by making a series of adjustments invoking all available experience with the particular materials. Adjustments that improve pumpability may also improve strength and economy. The ACI 304 report states that the addition of water does very little if anything to improve pumpability and may cause segregation. It is far better to find and correct deficiencies in the ingredients than to succumb to the costly and useless addition of water.