Sodium Silicate Moulding Material:

Moulds (and cores) might also be built from sand that attains its strength from the addition of 3 to 4% sodium silicate, a liquid inorganic binder that is also called as water glass. The sand might be mixed along the liquid sodium silicate in a standard muller and might be packed into flasks by any of the technique. This remains mouldable and soft until it is exposed to a flow of CO₂ gas, after that it hardens in a matter of seconds by the reaction.

Na₂SiO₃ + CO₂  Na₂CO₃ + SiO₂ (colloidal)

The CO₂ gas is odourless and nontoxic, and no heating is needed to drive the reaction. The hardened sands, although, have weak collapsibility, making shakeout and core elimination difficult. Unlike most other sands, the heating that take place as a result of the pour makes the mould even stronger (a phenomenon same to the firing of a ceramic material). Additionally, care ought to be taken to prevent the carbon dioxide in the air from hardening the sand before the mould-making procedure is complete.

A modification of the CO₂ procedure can be utilized when certain portions of a mould need higher strength, thinner sections, better accuracy, or deeper draws than can be attained with ordinary moulding sand. Sand mixed along sodium silicate is packed around a metal pattern to a depth of around 1 inch, followed by regular moulding sand like a backing material. After the mould is completely rammed, CO₂ is introduced through vents in the metal pattern. This hardens the adjacent sand, and now the pattern might be withdrawn with less possibility of damaging the mould.