9 Geopolymers are inorganic binders obtained by alkali activation of aluminosilicates. While the structure of 10 geopolymers is now well understood, the details of the geopolymerisation reaction and their impact on the rheology 11 of the paste remain uncertain. In this work, we follow the elastic properties of a paste made with metakaolin and 12 sodium silicate solution. After the first sharp increase of elastic modulus occurring a few hundred of seconds after 13 mixing and related to the heterogeneous formation of an alumina-silicate gel with a molar ratio Si/Al <4 located at 14 the grains boundaries, we focus on the progressive increase in elastic modulus on a period of few hours during the 15 setting of the geopolymer. In this study, we combine the study of rheological properties of the paste with 23 Na, 27 Al 16 and 29 Si static NMR measurement in order to better understand the origin of this second increase in elastic 17 modulus. Our results show that, after a few hours, Al and Na evolution in the liquid phase are concomitant. This