Powdered or particulate material, especially cement which is prone to caking, is stored in a fluidized storage container (1) and is conveyed in predetermined amount by conveyor means (15) to a mixer unit (20). The material is mixed with water which is also supplied to the mixer unit to form a grout which can be used in pump packing systems in underground mines. The invention provides simple equipment capable of reliably handling large quantities of cement, and is particularly suited for use underground in coal mines. (References to FIG. 1).