Abstract: A binder of this invention is a powder which comprises an intimate mixture of a copolymer of maleic anhydride with an olefinically unsaturated compound selected from the group consisting of an aliphatic .alpha.-olefin having 2 to 8 carbon atoms, styrene and methyl vinyl ether, 0.2 to 2.0 equivalents of a caustic alkali per carboxyl equivalent of said copolymer, and if desired, 30 to 500 parts by weight of an alkaline earth metal hydroxide per 100 parts of the total weight of said copolymer and said caustic alkali, and if desired, up to 300 parts by weight of additive per 100 parts of the total weight of said copolymer and said caustic alkali. A process for preparing a mold according to this invention comprises mixing said powdered binder with refractory particles and a small amount of water under agitation, and forming the resulting mixture into a shaped product, whereafter the shaped product is hardened by blowing CO.sub.2 gas therethrough.