Abstract: A gun for applying moistened refractory material to the interior surface of a furnace wall while the furnace is still heated includes an extended material tube or pipe long enough to reach into the furnace, and through this tube passes an airstream having dry granular refractory material entrained in it. Near its outer end the tube is encircled by a closure which defines an annular chamber to which water is supplied, and this chamber communicates with the interior of the tube through apertures arranged in at least one circumferential row so that the water in the chamber sprays into the tube and mixes with the refractory material. Beyond the closure the tube is fitted with a nozzle extension where thorough mixing of the water and refractory material occurs. A nozzle tip having an oval discharge opening is fitted onto the outer end of the nozzle extension and the moistened refractory material issues from the discharge opening. The tip may be straight or at an angle.