(57) 57 A machine for spraying cement or plastic based materials for building purposes comprises two separate portions. A hopper portion comprises a frame 10 with a hopper 11 and pump 26 driven via a flexible coupling and shaft 25 from an air motor 20 controlled via a control unit 21 from the end (not shown) of the spray pipe. A mixing portion comprises a frame 40 with a mixing chamber 60 mounted thereon, the mixing chamber containing mixing paddles driven by a second air motor mounted on the frame 40 (Figure 4). The base of the frame 40 fits into one end of the hopper 12 and can be bolted thereto by bolts through the holes 15,41. The two portions can be separated quickly for servicing if either breaks down, and a conventional mixer can be used temporarily with the hopper portion (Figure 1).