Abstract: An attachment for a slip forming paver for automatically finishing concrete surfaces which includes an elongated concrete smoothing trowel member. A mechanism is provided for oscillating the trowel member back and forth along its longitudinal axis and includes another mechanism for moving the oscillating mechanism and the trowel member itself transversely with respect to such longitudinal axis. The trowel member is pivotally mounted to the oscillating mechanism by a pair of levers and a winch and cable mechanism is provided for selectively adjusting the effective weight of the trowel member with respect to the concrete being smoothed by the trowel member. A turnbuckle arrangement is provided for adjustably maintaining the lower surface of the trowel member straight and smooth by applying tension forces thereon. To the extent that the weight adjusting mechanism and the turnbuckle arrangement move the trowel member out of balance, a single weight is provided, on the end opposite the winch.