An apparatus for mixing an additive into a fluid to form a settable mixture includes a main fluid passageway having an inlet for receiving a supply of the fluid and an outlet for dispensing the fluid, the passageway having a longitudinal axis. The apparatus includes a control valve defining a portion of the main fluid passageway and configured for selectively controlling the flow of fluid in the passageway, an additive injector disposed in the passageway and having an emitter disposed in close relationship with the axis and oriented toward the outlet. A static mixer is disposed between the injector and the outlet for enhancing the uniform mixing of the additive and the fluid. Connection points between the inlet, the valve and the static mixer are configured for smooth transition of fluid and the prevention of at least one of the collection and premature setting of the mixture.