Method for constructing molds and cores layer by layer by means of a binder containing water glass, and a binder containing water glass

A binder, comprising

• water glass with a molar ratio of Na2O/M2O of greater than 0.4, preferably greater than 0.5 and more preferably greater than 0.6 and particularly preferably greater than 0.7, and a molar modulus SiO2/M2O of greater 1.4 to less than 2.8, preferably greater than 1.6 to less than 2.6, preferably greater than 1.8 to less than 2.5 and more preferably greater than 1.9 and less than 2.4,
• wherein in each case M2O is the sum of the molar amounts of lithium, sodium and potassium calculated as oxide, based on the amorphous alkali silicates, alkali oxides, alkali hydroxides, alkali phosphates and/or alkali borates contained in the binder;
• and
• wherein any particulate constituents in the binder have a D90 value of less than 70 μm;
• the binder contains at least one phosphate or at least one borate or phosphate and borate;
• and
• the binder has a dynamic viscosity at 25° C. of greater than 1 mPas and less than 25 m Pas.