Abstract: Water-activatible tapes are disclosed comprising a substrate of fibrous or foamed plastics material impregnated or coated with a water-reactive cementitious composition which is reactive with water to form a set mass, the composition containing at least one cement, especially Portland cement, a non-water sensitive polymeric binder, such as a natural or synthetic rubber, and a water-sensitive additive which is compatible with the polymeric binder and is sufficiently water-sensitive to at least swell in contact with water. The tapes are suitable for construction purposes, e.g. sealing joints in buildings or pipe-wrapping, by wetting with water to form a pliable mass which can be deformed to the desired shape and which will subsequently harden.