Abstract: The invention provides a filler gun suitable for injecting a mixture of particulate solid and liquid binder into a cavity, for example the wall cavity of a building, which comprises a hollow body having an outlet at one end, a binder inlet for liquid binder at the other end, and a side inlet for granular or particulate solid, which side inlet is directed towards the outlet at an angle of less than 90.degree. with respect to the direction of flow of liquid binder from the binder inlet to the outlet in operation of the gun, wherein an outlet sleeve is releasably located in the body between the side inlet and the one end and an inlet sleeve is releasably located in the body between the side inlet and the other end, the inlet sleeve having an axial bore and a side passage opening into the bore which passage is adapted for the reception of a liquid binder supply line, and the body is slotted to enable withdrawal of the inlet sleeve therefrom without prior detachment of the supply line.