A settable composition comprising (i) a cementitious component comprising at least 25% of calcium aluminate of which at least 40% is calcium monoaluminate said cementitious component optionally containing one or more particulate fillers but containing less than 10% by weight of calcium sulphate, the % being by weight being based on the weight of the cementitious component and (ii) an aqueous emulsion of an organic polymer, the amount of (ii) in relation to (i) being such as to provide a weight ratio of polymer solids to weight of (i) of from 0.5:1 to 10:1, preferably 0.6:1 to 2.5:1 or (iii) a dispersible organic polymer and where the amount of dispersible polymer is such as to give a weight ratio of polymer to weight of (i) of from 0.5:1 to 10:1, preferably 0.6:1 to 2.5:1. The cementitious component (i) preferably contains an amount of fiber effective to improve the tensile strength of coatings obtained from the settable composition but not exceeding 5% by weight of the cementitious component (i). The dry composition comprising parts (i) and (iii) above can be mixed with water in the mine.