Abstract: A sandblasting system including two principal components, a trolley which is located on the flat upper surface of the object to be sandblasted and a blasting machine with an oscillating blast nozzle that is carried by the trolley. For cleaning vertical surfaces, the blast machine is suspended from hoist cables, whose ends are carried by the trolley. The blast machine includes a hoist drum for gathering or releasing the cable to raise or lower the blast machine along the vertical surface. For cleaning horizontal surfaces, the blast machine is carried by the trolley itself and oriented so as to direct the sand blast in a downward direction. The blast machine carries a mechanism for oscillating the blasting nozzle and the hoist drum within a housing to protect the moving parts from the harsh operating environment. The invention is particularly suited for the sandblasting of petroleum product storage tanks.