A water-resistant composition 20 includes a graphene material 22 forming a matrix with a resin 23. The matrix can include reinforcing fibres such as glass fibres. The composition can include the graphene material 22, a polyester resin 23 and glass fibre reinforcement. Multiple forms of the composite can be provided in layers, such as a barrier layer containing the graphene material 22 in a resin 23 and a second layer containing reinforcing material. A cosmetic coloured gel coat can be applied to the composition and a clear gel coat applied over the cosmetic coating. The graphene material can include graphene platelets 22 dispersed within the resin. The graphene material can provide up to 5% by weight (% wt) of the composite, preferably up to 2% wt of the composite, more preferably between 1% wt and 2.5% wt of the composite and yet more preferably 2% wt of the composite. The composition can be applied to a boat hull, a pipe, a swimming pool, a spa or a tank, or a surface subject to prolonged contact with or submersion in water.