Abstract: A method for working a concrete surface uses a water jet ejected from a nozzle of a nozzle holder. The nozzle holder reciprocates in cutting sweeps and moves together with a working apparatus in steps between the cutting sweeps. The water jet is directed in directions of the sweeps, and at the end of each sweep, the nozzle holder is swung into a new angle of attack for a subsequent cutting sweep. At the end of a cutting sweep, the nozzle holder begins to swing backwards simultaneously as its linear velocity increases to permit the target area to remain substantially unchanged at the start of the stepping of the working apparatus so that the water jet makes a cut forwardly in the stepping direction. The stepping and change of angle of attack are completed simultaneously immediately prior to the commencement of a subsequent cutting sweep.

Abstract: One cuts away the surface layer of a concrete surface, for example the roadway of a concrete bridge, by using a water jet ejected out of a nozzle 31 on an elongated nozzle holder 30. One reciprocates the nozzle holder in cutting sweeps and moves the entire machine in steps between the cuttin sweeps. The water jet is directed obliquely forwardly in the directions of the sweeps and, at the ends of the sweeps, the nozzle holder is swung to its new angle of attack for the subsequent cutting sweep. When the water jet reaches the end of the cutting in a cutting sweep, the nozzle holder begins to swing backwards at the same time as its linear velocity increases so that its target area will remain unchanged or almost unchanged at the same time as the stepping of the machine starts so that the water jet will make a cut 34 forwardly in the direction of stepping. The stepping and the change of angle of attack are finished simultaneously and a new cutting sweep starts directly.