A surface-treating apparatus has a dual-purpose surface-treating blade assembly that includes a blade holder for holding and loading a blade member, and a one-piece blade member having a first edge mounted to the blade holder and a second edge for contacting and treating a surface. The one-piece blade member has a mid-portion for applying a first edge-loading force to lightly contact and remove random spots from a central imaging region of the surface, a first end portion, and a second end portion. The dual-purpose blade assembly also includes a first shim device and a second shim device assembled respectively to the first end portion and to the second end portion of the blade member for stiffening such end portions and increasing a magnitude of each of a second and a third different edge-loading forces at such end portions relative to the first edge-loading force.