Disclosed are aspects of board finishing systems. For example, in various aspects, disclosed are joint compound compositions, wall assemblies, methods of treating walls, and products related to any of the foregoing, including reinforcement trim, e.g., for protecting corners where boards meet, fasteners, and tape. The joint compound preferably is a drying type composition with reduced shrinkage property, and includes binder and hollow spheres, resulting in an ultra lightweight formulation in some embodiments. The joint compound composition can be applied in a one-coat treatment in preferred embodiments. Other aspects of board finishing system accommodate such a one-coat treatment to thusly allow a user to manipulate the compound closer to the plane of board as compared with conventional formulations. Joint tape and reinforcement trim can include non-swelling synthetic paper facing material in some embodiments.