Mixing apparatus comprising a batch mixing vessel (45) with an inlet (40) to receive constituent material, an agitation assembly for mixing the constituents and an outlet to convey batches of the mixed is provided. The apparatus includes means (120) for pressurizing the vessel to assist in evacuation of the mix, and a conduit (210) through which the mix is conveyed. A single pneumatic source is used both to pressurize the mixing vessel and to drive a jet pump (62) comprising the batch loading means. During the mixing cycle, the compressor used to discharge the finished mix is generally idle. It has been discovered, that this compressor can be used during these periods to drive a jet pump to load the mixing vessel. Therefore, manual loading is avoided and can be achieved such that the mixing cycle time is not interrupted.