A spray urethane gun assembly having a main body with a bore and a mixing chamber. An elongated spool is longitudinally, slidably mounted in the main body bore and movable between an extended position and a retracted position by an actuator. A first and a second inlet port are formed in the main body and a first and second outlet port are also formed in the main body. A first axially extending fluid passageway is formed in the spool and this first fluid passageway fluidly connects the first inlet port with the first outlet port when the spool is in one of the retracted or extended position, and fluidly connects the first inlet port with the mixing chamber when the spool is in the other of the retracted or extended position. A second axially extending passageway is formed in the spool and this second fluid passageway fluidly connects the second inlet port with the second outlet port when the spool is in one of its retracted or extended position, and fluidly connects the second inlet port with the mixing chamber when the spool is in the other of its retracted or extended position. A dispensing port formed in the main body is open to the mixing chamber for dispensing the fluid mixture within the mixing chamber.