A power tool (10) is provided having a plastic casing (12) and a scraper blade (14). The blade (14) is caused to reciprocate by an internal low power rotary motor (24) which drives a cylinder cam (28) having a sinusoidal cam track (34). A pair of studs (36) ride in the cam track (34), and drive the reciprocal movement of the blade (14). The tool (10) is substantially sealed against liquid ingress by means of an elastomeric membrane within the casing (12), and may be used as a marine growth remover, for defouling boats and the like.