Abstract: A nozzle arrangement for a high pressure jet for use in a device for treating surfaces by removing material from, roughening or cleaning such surfaces comprises a nozzle having an elongate body which is rotatable about its longitudinal axis. A nozzle head inclined at an angle of approximately 30.degree. to the longitudinal axis of the nozzle body communicates with the interior of the nozzle body and a high pressure pump is provided for generating a high pressure liquid jet to issue from the nozzle head. The nozzle head is maintained at a substantially constant distance from a planar surface to be treated and the nozzle body is reciprocated in partial rotations about its longitudinal axis in opposite directions to cause the high pressure jet issuing from the nozzle head to strike the surface to be treated with a recurring arc-shaped pivoting movement.