An impact hammer (1) for breaking a working surface (5), the hammer including a drive mechanism (11, 12, 14) and a housing (6) with an inner containment surface (8) and a reciprocating hammer weight (9). A reciprocation cycle of the hammer weight (9) includes an upstroke and a down-stroke, the hammer weight (9) respectively moving upwards and downwards. On the down-stroke the hammer weight (9) impacts a striker pin (4) with a driven end (17) and a working surface impact end (18). A vacuum chamber (22) in the housing is formed by the containment surface (8), upper vacuum sealing (24) coupled to the hammer weight (9) and lower vacuum sealing (25). The hammer weight (9) is driven toward the striker pin (4) by the pressure differential between atmosphere and the vacuum chamber (22) formed on the upstroke. A down-stroke vent (43) permits fluid egress from the vacuum chamber (22) on the down-stroke.