Modified colloidal silica in silicate paints

Céline de Lame and Jean-Marie Claeys, CoRI, Belgium

Peter Greenwood and Hans Lagnemo, Eka Chemicals, A business Unit within AkzoNobel, Sweden

Mineral silicate paints have been used for long time to protect buildings (mineral substrates) or to restore old monuments. These inorganic paints, after water evaporation, reaction with carbon dioxide and humidity from air, are chemically bonded to mineral substrates and petrify with the substrate to an insoluble combination. This process is named silification. Silicate mineral paints have a lot of advantages like high durability due to their inorganic composition, scrub resistance, high vapour water permeability, resistant to mould and fungal growth due to their high alkalinity, odourless, non flammable, free of solvents and biocides, environmentally friendly. Their major drawbacks are high water absorption and low flexibility.

This study has investigated the use of modified colloidal silica in mineral silicate paints in place of a part of the inorganic binder (silicate potassium) on final properties of this kind of paints. The ability of such modified colloidal silica to modify final properties has been evaluated from chalking resistance tests, liquid water permeability, scrub resistance, dirt pick-up resistance, adherence and König hardness. It has been highlighted that modified colloidal silica induces especially a strong reduction of the liquid water permeability and improvement of the adherence without affecting badly the other properties. These paint reinforcements can be related to the modifications of film surface properties and internal stress.