To quickly cut back the filler, we worked it with a Surform file before it fully hardened. The rounded profile files are superior to the flat versions. The proper technique is to run the file at a 30- to 45-degree angle rather than straight across. Ideally, the surface will be close to level at the same time that the surface has uniform file marks and the edges are broken or feathered all the way around. If the surface is level but there are low spots that haven't been hit with the file, another application of filler will be needed.