Abstract: A composition for use as a liner, in particular for preventing spalling of rock particles and falls of ground at rock excavation sites, for the lining of swimming pools or any other water proofing application such as concrete coating for corrosion and environmental damage protection is provided. The composition includes a water-based dispersion of polyurethane and a cementitious material. The cementitious material and the dispersion are mixed together to form a polymer concrete comprising an interpenetrating network of inorganic and organic polymers. Anhydrous calcium sulphate forms part of the cementitious material to improve the hardening and curing properties of the liner. Epoxy is a further component of the liner, thereby to improve the adhesion properties of the liner.