A method is disclosed for preparing and dispensing a mixture obtained by mixing at least one first chemically reactive component and at least one second chemically reactive component containing a dispersed solid material by a high pressure mixing device comprising a mixing chamber for mixing the components, in which a valve member is slidable, in particular a slide-valve, provided with longitudinal slots for recirculating the components to respective storage tanks. The method provides removing from at least one tank, a dosed quantity of the at least second chemically reactive second component to with filler material is added; recirculating the second component through the slots of the slide-valve for a period of time that is comparatively very reduced with respect to a recirculating step of the at least first component through the slide-valve. An apparatus for preparing and dispensing the mixture is also disclosed.