A prefill tool for finishing wallboard joints is provided for finishing a wallboard joint, and includes a box assembly defining a hopper, having a top wall and a front wall constructed and arranged for engaging the wallboard joint. The front wall partially defines a gate dimensioned for dispensing joint compound stored in the hopper. Also, the gate is located on a skid plate mounted on the front wall, the skid plate having a main portion, and a gate portion partially defining the gate being displaced from a plane defined by the main portion.