A scarifying rig may be mounted on the surface of a floating roof to move about the perimeter of the roof. The rig comprises a trolley, one or more support rails fixed on the trolley, and a horizontal arm mounted on the support rails for controlled movement along the support rails. A vertical rail is attached substantially to the end of the horizontal arm for reciprocating vertical movement (up and down) about the end of the horizontal arm. A nozzle assembly is mounted to the vertical rail.