A vertical mixer assembly for mixing a bulk material is disclosed. The vertical mixer assembly comprises a floor having an upper surface； at least one wall extending from the floor and having an interior surface and an upper edge； the floor and the at least one wall defining an open topped mixing chamber having a general tub-shape suitable for receiving the bulk material； at least one vertical auger positioned in the mixing chamber for mixing the bulk material, the auger having a flight suitable for mixing the bulk material upon operation of the auger； an opening in the mixing chamber for allowing egress of the bulk material, the opening having a wall portion and a floor portion； and a door assembly. The door assembly allows for more consistent unloading of the mixed bulk material and for quicker unloading of the mixed bulk material. The door assembly comprises a side door moveable between a closed position covering the wall portion of the opening and an open position exposing the wall portion of the opening； and a floor section moveable between a closed position covering the floor portion of the opening and an open position exposing the floor portion of the opening.
