The pilot was attempting the first landing of the day on an airstrip which was about 800 metres in length. It had appreciable longitudinal slope and the surface was covered in long wet grass. The landing direction was up hill with a quartering tail wind from the left. The pilot reported that the aircraft touched down about half way along the strip and that he anticipated the slope would provide the necessary retardation. As the roll progressed, it became apparent the aircraft could not be stopped on the remaining strip so a ground loop to the left was initiated. The aircraft slid sideways into a Superphosphate dump at the end of the strip and damaged the right aileron, right fuselage and tailplane.