Method and composition of binder for manufacturing sand molds and/or cores for foundries

A binder for the production of sand cores and/or molds for foundries that includes sand mixed with an alkyl silicate, preferably tetraethyl silicate; an aqueous solution of an alkali metal silicate, preferably sodium silicate, which solution also contains an alkali metal hydroxide, preferably sodium hydroxide, where the ingredients in such mixture are preferably in given percentage ranges and are mixed until the sand shows a homogeneous aspect and constitution. Also method of manufacturing sand molds for foundries that includes mixing foundry sand with the aforementioned binder, blowing the sand mixed with the binder, having still between 0.5% to 2.5% of water, into a cold box by means of air that is at room temperature, and once the cold box mold has been filled with the sand, passing a hot air current through the sand to dry and harden the binder thus obtaining the foundry mold.