Observations have shown that the state of preservation of mosaics in the 6th Century churches of Gerasa (modern Jarash) is generally better than the later ones that date to the 7th century. An investigation of the composition and texture of the mortars used in the production of the mosaics was undertaken in order to understand the reason for this.The mortars used were lime mortars. These were produced through the calcination of local limestone and the prolonged slacking of the resulting lime. Laboratory analyses of the mortars have allowed the tracing of changes in relationship between the quality of the mortar and its microscopic and compositional characteristics through the time period studied. This helped to understand variations in mortar preparation techniques and raw materials used. The analyses have shown a great variation in composition and texture within a relatively short period of time, which may be attributed to socioeconomic and political factors, as no depletion of raw material is plausible (except, perhaps fuel).