  Historical monuments, outdoor stone sculptures and artworks made of porous
materials are exposed to chemical and physical degradation over time.
Presently, the most promising route for consolidation of weakened porous
materials is the injection of viscoelastic solutions of polymerizing compounds.
Those compounds, after injection, undergo a sol-gel transition inside the
porous media through evaporation of the solvent. Finding a suitable gelifying
solution as a consolidant calls for understanding the drying kinetics of
viscoelastic fluids in porous media. Here, we present a multiscale study of the
drying kinetics of solutions during the sol-gel transition. We investigate the
drying dynamics and subsequent water uptake of a gel using NMR and X-ray
microtomography techniques in porous materials. We find that during drying, a
distinct front develops which separates the liquid region from the gelled
region. This front advances from the free surface of evaporation towards the
inner parts of the stone. We identify different drying periods which appear to
be dependent on the intrinsic properties of the porous medium influencing
strongly the homogeneity of the final gel distribution within a treated stone.
Our findings not only are relevant for the consolidation of porous artworks but
also for civil and soil engineering processes where the fluids considered are
generally more complex than water.
