Abstract: An abrasive cleaning or cutting apparatus and method suitable particularly for underwater use at relatively low nozzle (19) overpressures (e.g. conveniently up to about 7 kg/cm.sup.2 above local hydrostatic pressure). The pressurized mixing zone (1) in which abrasive particles from hopper (3), compressed air from air-line (2), and water from water supply line (15) are mixed to form the abrasive stream is arranged such that the abrasive stream includes abrasive particles at least partially surface-wetted by the liquid entrained in air or an air liquid mist as an abrasive carrier. Preferably about 5 to 10% of the liquid is in the mist the remainder going to encapsulate the abrasive particles. The apparatus also includes valves suitably automatically actuable (in response to signals from an underwater sensor) to shut off the surface apparatus from the abrasive-carrying pipeline to restrict or prevent reverse flow in the pipeline should the mixing pressure drop at the surface.