A spray gun assembly for applying a coating with plural components includes a nozzle, a main pneumatic inlet, an atomizing air flow path, a fan air flow path, a colloidal feed inlet, an internal atomizing outlet, a pressurized feed inlet, and a catalyst outlet. The nozzle includes a main atomizing outlet and a fan air outlet. The main pneumatic inlet receives compressed air from a compressed air source. The colloidal feed inlet receives a colloidal suspension component of the coating via gravity feed from a gravity feed container. The pressurized feed inlet receives a catalyst component of the coating from a pressurized feed container. The catalyst outlet expels the catalyst component in the fan air flow path proximate the nozzle. A method for applying a coating with plural components is also provided. A system includes the gravity feed container, the pressurized feed container and the spray gun assembly.