An apparatus for impacting on a hard surface such as concrete so as to break up the hard surface. This apparatus comprises a frame having a bed and an upstanding rail assembly projecting from the bed, a drive shoe, a hammer means attached to the rail assembly so as to be movable in only one direction and operatively connected to the drive shoe for impacting upon the drive shoe. The drive shoe lies adjacent the surface so that upon impact from the hammer means, the shoe forcefully impacts the surface so as to break up the surface. An adjustment means is used to selectively position the drive shoe relative to the hammer means.