The invention provides a method of breaking a hard material such as rock including the steps of drilling a plurality of holes (2) in the face (1) thereof; inserting at least two cartridges (3) containing gas generating means into each of the holes (2), the cartridges (3) being spaced by a stemming material (2) such as a particulate material; stemming the cartridges (3) in the hole (2); and activating the means.
