The invention concerns a method and a device for repairing quay-protecting linings and similar structures. According to the invention a support mould (3) having an L-shaped cross-sectional configuration is attached to the external face of the quay-protecting lining, whereupon into said mould is inserted a lining sheeting having projecting gripping means (16) thereon, whereupon the casting compound is poured into the gap between the original quay-protecting lining (1) and the lining sheeting (4). After hardening of the casting compound the support mould is removed, the lining sheeting then forming a protective facing turned towards the water.