In a painting operation, a method for controlling the viscosity of a coating composition wherein said coating composition is a sprayable mixture, said method comprising the steps of: producing a first atomized stream of a first coating component of said coating composition through an orifice of said spray gun with a stream of a pressurized carrier, wherein said first coating component is stored in a first storage container and conveyed through a first inlet of said spray gun to said orifice and wherein the viscosity of said first coating component remains substantially constant prior to being conveyed through said first inlet; producing a second atomized stream of a second coating component of said coating composition, wherein the second atomized stream is produced by siphoning the second coating component with a siphoning stream selected from the stream of the pressurized carrier, or a combination of the stream of the pressurized carrier and the first atomized stream of the first coating component, from at least one delivery outlet coupled to a second storage container containing said second coating component, said orifice being relatively positionable with respect to said delivery outlet to siphon the second coating component with different siphoning stream depending on the relative position between the orifice and the delivery outlet; optionally, regulating the supply of the second coating component to said delivery outlet by coupling a regulatory device to said delivery outlet; intermixing the first atomized stream and the second atomized stream to form a coating mixture; and applying the coating mixture on the substrate to form the layer of said coating composition thereon; and wherein the coating composition comprises protected crosslinkable functional groups, and wherein said first coating component is mixture of a crosslinkable component and a crosslinking component. producing a first atomized stream of a first coating component of said coating composition through an orifice of said spray gun with a stream of a pressurized carrier, wherein said first coating component is stored in a first storage container and conveyed through a first inlet of said spray gun to said orifice and wherein the viscosity of said first coating component remains substantially constant prior to being conveyed through said first inlet; producing a second atomized stream of a second coating component of said coating composition, wherein the second atomized stream is produced by siphoning the second coating component with a siphoning stream selected from the stream of the pressurized carrier, or a combination of the stream of the pressurized carrier and the first atomized stream of the first coating component, from at least one delivery outlet coupled to a second storage container containing said second coating component, said orifice being relatively positionable with respect to said delivery outlet to siphon the second coating component with different siphoning stream depending on the relative position between the orifice and the delivery outlet; optionally, regulating the supply of the second coating component to said delivery outlet by coupling a regulatory device to said delivery outlet; intermixing the first atomized stream and the second atomized stream to form a coating mixture; and applying the coating mixture on the substrate to form the layer of said coating composition thereon; and