An apparatus for producing a three-dimensional object by spray deposition including a powder conveyance line A arranged to channel a flow of spray material entrained in a carrier gas to a nozzle (a first flow). The apparatus also has a process line B arranged to channel a flow of gas to the nozzle (a second flow). The apparatus also has a spray nozzle. The apparatus is such that pressure and temperature parameters of the first flow are controlled in real time, but for the second flow these parameters are not controlled in real time. The two flows merge to cause spray material to be propelled from the nozzle to a substrate to create a three-dimensional object.