Grout injection is a technique commonly used in the repair and strengthening of masonry, due to the simplicity in its execution. However, to design a suitable grout, a proper methodology must be followed. The grout must accomplish requirements that depend mainly on mechanical behaviour and durability features of the struc-tures. Grouting can be also applied to earthen structures, for repairing cracks and filling voids. The same methodology can be used to design grouts, but the requirements must be adapted. Therefore, this paper pre-sents a discussion concerning the repair and strengthening of masonry and earth constructions through grout injection. To emphasize the differences in the requirements, first a short characterization of earth as a building material is given. Subsequently, the main decay phenomena are identified. Finally, attention goes to the effect of shrinkage and swelling behaviour of earth and the design of an appropriate grout for injection.Fundação para a Ciência e a Tecnologia (FCT
