[[Image:percussion gouge.jpg|thumb|right|200px|percussion gouge]]
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The Stone Hammer is a form of [[Percussion - general|percussion drilling]], used when boulders or hard clay is encountered. A hollow drill bit is attached to a hammering tool. The hammering tool consists of a heavy weight which moves up and down in a pipe. Once the bit and hammering tool are lowered into the borehole by a cable, the same cable can be used to do the hammering. Lifting and dropping the hammer drives the drill bit down. When 60cm has been drilled, the unit is pulled up to the surface to empty the hollow drill bit. The stone hammer is only successful when boulders are encountered, not in homogeneous or solid stone layers were , where displacement of the material is not possible.
In western counties Western countries the same principle is used with the percussion gouge. As opposed to the stone hammer, the hammering action of the percussion gouge takes place on ground level. The gouge is electrically driven and used to break hard surface layers (rubble) and to take soil samples.
The stone hammer and percussion gouge are not individual drilling methods, but used to supplement other methods when boulders, rubble or hard clay is encountered during drilling. Although it does not penetrate very hard stone such as basalt, it is a tougher option than other options such as the [[Rota sludge well drilling|Rota-sludge method]] or the [[EMAS well drilling | EMAS method]].
The Stone-hammer method has won a competition for innovative irrigation technologies organized by the World Bank, Winrock and International Development Enterprises (IDE).
===Suitable conditions===