The invention generally relates to a flat box finisher for applying mud (or mastic or joint compound) over taped joints on walls and ceilings. Usually, paint or wallpaper is then applied over the finished mud. The flat box finisher has no external springs, but has at least one internal support bar which acts as a spring for applying pressure to a corresponding dry wall finishing handle affixed to the flat box finisher. The internal support bar is surrounded by the mud while the device is in use. As a result of having no external spring, the flat box finisher may be reduced in size for smaller jobs or difficult to reach areas of a room. The internal support bar may also eliminate problems with external springs, such as the spring wearing out or becoming damaged during use or storage.