Abstract: An apparatus for mixing a cement slurry with a glass fiber in order to produce a glass fiber reinforced cement, including a spray gun, apparatus for cutting the glass fiber and apparatus for feeding the cut fibers to the spray gun. The spray gun comprises a glass fiber supply passage, a cement slurry supply passage, an air introduction passage, a plurality of air introduction holes communicated with the air introduction passage for injecting compressed air into the cement slurry supply passage and a closing element having at least two injection holes communicated with the cement slurry supply passage. The cement slurry is injected together with the compressed air through the injection holes and is mixed with the cut glass fibers discharged from a discharge opening of the fiber supply passage.