Surface treatment operations, such as sanding, deburring, finishing, grinding, polishing, etc. are progressively becoming more automated using robotic systems. However, previous research in this field used a completely automatic operation of the robot system or considered a low degree of human-robot interaction. Therefore, to overcome this issue, this work develops a truly synergistic cooperation between the human operator and the robot system to get the best from both. In particular, in the application developed in this work the human operator provides flexibility, guiding the tool of the robot system to treat arbitrary regions of the workpiece surface; while the robot system provides strength, accuracy and security, not only holding the tool and keeping the right tool orientation, but also guaranteeing a smooth approach to the workpiece and confining the tool within the allowed area close to the workpiece. Moreover, to add more flexibility to the proposed method, when the user is not guiding the robot tool, a robot automatic operation is activated to perform the treatment in prior established regions. Furthermore, a camera network is used to get a global view of the robot workspace in order to obtain the workpiece location accurately and in real-time. The effectiveness of the proposed approach is shown with several experiments using a 6R robotic arm.