Abstract: A controlled method of, and apparatus for, continuously processing initially dry, particulate, cementitious material and fly ash solids and mixing them with a liquid to provide a liquid slurry of consistent proportions. The method and apparatus are concerned with a bin system for the fly ash solids and dry cementitious solids, opposed conveyor flight elements within the bin system leading to a metering valve system, a conveyor system for receiving the fly ash and cementitious material solids in metered proportions and then mixing them with a liquid to form a slurry, a conduit for pneumatically supplying solids entrained in an airstream to the bin system, a pressure controlled system for egressing air from the bin system and separating remaining solids from the air while maintaining the bin system under less than atmospheric pressure, and controls for monitoring the volume of material in the bin system.