Rheology optimization of particle modified consolidants

Ethyl silicate-based consolidants are used to restore strength to degraded stones. One of the limitations of strength development using these products is their reported cracking behavior during drying. Particle Modified Consolidants (PMC) consist of a silicate matrix plus colloidal oxide particles. The presence of particles physically limits the silicate network from shrinking under capillary pressures, and thereby reduces strength loss during drying. In addition, the network maintains a higher permeability, because the dried consolidants remains porous. When the particles used are pigments, it is also conceivable to adjust the consolidant color. Moreover, a careful choice of particles should allow matching the thermal dilatation of the consolidant to that of the stone. An important limitation to further development of PMC has been the ability to avoid particle agglomeration in the dispersion. When agglomerates are present, not only do they increase the viscosity but they also can block pore entrances, preventing consolidant from entering the stone. In this work we demonstrate the feasibility of adsorbing nano-silica particles onto pigment particles to create a steric barrier to agglomeration. Rheology and density measurements confirm that the resulting dispersion is fluid and stable against settling. The consolidant readily penetrates Ohio Massilian sandstone, providing improved strength, stiffness, and salt resistance, compared to a commercial silicate consolidant.