A finishing trowel comprised of a blade, a mounting and a handle, wherein the handle is hollow and has a square mounting hole for receiving a square mounting surface. A plastic handle is comprised of a durable inner core material and a grippable outer member. The handle's inner core includes deformable ribs which axially line the mounting hole and provide a secure, lash-free fit onto the mounting surface over a broader range of manufacturing tolerances for the parts. The handle also includes an endcap which cuts into and seals the endcap against an outer grippable material upon tightening of a flanged nut onto the mounting. A lip extends from the handle and encompasses a portion of the mounting to facilitate increased torque transfer from the handle to the mounting and blade. The replaceable handle can also be formed of other grippable materials such as wood.