Abstract: A waterbar for use between adjacent panels (22, 24) in a diaphragm wall, the waterbar comprising a first member (5) in the form of an elongate strip (6) provided along a first longitudinal edge (8) with a hydrophilic material (7) and along the opposite longitudinal edge (9) with a retaining channel (10), and a second member (12) in the form of an elongate strip (13) provided along a first longitudinal edge (15) with a hydrophilic material (14) and along the opposite longitudinal edge (16) with a keying projection (17). The retaining channel (10) of the first member (5) is shaped so as to slidably retain the keying projection (17) of the second member (12), and either the retaining channel (10) or the keying projection (17) is provided along its length with a hydrophilic material (18), which serves to seal the joint between the first and second members (5,12).