Use of a particulate material comprising a particle-shaped synthetic amorphic silicon dioxide as an additive for a molding material mixture, corresponding method, mixtures, and kits

A process for producing a hot-cured molding having increased moisture resistance, having the following steps:

• (i) producing a molding material mixture by mixing together at least the following constituents:
• refractory mold base material having an AFS grain fineness number in the range from 30 to 100,
• particulate amorphous silicon dioxide, wherein the particulate amorphous silicon dioxide has a particle size distribution with a median in the range from 0.7 to 1.5 μm, determined by means of laser scattering, and
• water glass,
• (ii) forming the molding material mixture, and
• (iii) hot curing the formed molding material mixture, so as to result in the molding,
• wherein
• the constituents of the molding material mixture are additionally mixed with a particulate material as additive comprising, as its sole constituent or as one of multiple constituents, a particulate synthetic amorphous silicon dioxide, wherein the particulate synthetic amorphous silicon dioxide has a particle size distribution with a median in the range from 0.1 to 0.4 μm, determined by means of laser scattering.