Coating composition for the foundry industry, containing particulate, amorphous silicon dioxide and acid

A coating composition comprising

• (a) an aqueous phase having a pH less than 4.5,
• (b) particulate, amorphous silicon dioxide, and
• (c) one or more further refractories,
• for producing a coating on a waterglass-bound mold or a waterglass-bound core, for use in the foundry, where the coating composition possesses a fraction of particulate, amorphous silicon dioxide of constituent (b) in the range from 1 to 18 wt %, and where the constituent (c) comprises one or more substances selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, phyllosilicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide, and bauxite,
• wherein the particulate, amorphous silicon dioxide comprises primary particles and the primary particles of the particulate, amorphous silicon dioxide of constituent (b) possess a D90 ranging from 1 μm to 10 μm, determined by laser diffraction.