Abstract: This invention relates to a method of post preparation of an injection compound which is useable for injection in for instance existing rock cracks or cracks arisen in connection with blasting away rock during for instance tunnel driving, the injection compound having been subject to a preparation, leading to that the injection compound has been given qualities with regard to shape of the crack formations of the rock. According to the invention, the method is characterized in that the injection compound is subjected to a post preparation in the form of a passage through a wire netting, the size of the mesh and the wire dimension of which being determined from a judgement of the following points: the size of the cracks and the cavities in the rock; the tendency of the injection compound to build up filter cakes; desired rheological qualities of the injection compound. The invention also relates to a device for making the method possible.