a method and installation for forming a coating on a substrate , wherein the substrate is contacted with a gas treatment atmosphere in order to carry out said coating . the gas treatment atmosphere includes a primary gas treatment mixture comprising excited or unstable gaseous species obtained from a device which converts an initial gas mixture into said species , and an adjacent gas treatment mixture comprising at least one gas precursor required to form said coating , whereby the adjacent mixture is not transported via said device . the adjacent gas treatment mixture is injected into the flow of the primary gas mixture when the gas exits from the device .