Abstract: The invention concerns a pumpable cementitious composition containing porous light weight aggregate. The composition is rendered pumpable by the addition of a dispersing agent and a gelling agent in sufficient amount to reduce the absorption of water by the aggregate when the composition is pumped. In particular, the dispersing agent is a sulphonated melamine or naphthalene formaldehyde or a sulphonated polystyrene, and the gelling agent is a water soluble cellulose derivative such as methyl cellulose, the two agents each comprising 0.001% to 0.04% by weight of the composition.