An accelerating admixture for use with spraying cementitious compositions such as shotcrete comprises (a) a compound selected from aluminium hydroxide and aluminium hydroxysulphate and (b) an acidic substance which essentially does not react with the compound. The preferred acid substances are organic acids. The compositions may also comprise ethylene glycol, a polymer comprising carboxylic moieties, an amine e.g. alkanolamine and a superplasticizer.
