Water-based - involves water sprays, with or without pressure, hot or cold, for
varying periods of time. This removes surface dirt or softens it to make brushing
effective. Most effective on limestones.
Blasting - usually involves blasting sand, both wet and dry, but various materials can be used including ice.
Abrasive - involves using abrasive tools, needle guns, discs and cones, all of which basically involve dressing back the surface of the stone.
Chemicals washing - use of acidic and alkaline solutions. Most commonly applied to sandstone.
Poulticing - applying pastes, acid, alkaline or neutral to facades.
There are a number of texts on the subject, the most rational of which is Nicola Ashurst's two
volume "Cleaning Historic Buildings".