Abstract: A method is provided for producing polyurethane-based cores and moulds, using a mixture of particle-formed material such as sand, a bonding agent containing a polyisocyanate compund and a polyhydroxy compound and if necessary a solvent, after which the mixture is shaped to a desired form and hardened by means of a catalyst, wherein the polyhydroxyl compound consists of one or more aliphatic or aromatic polyethers, together with a hydroxyl compound for initiating the catalyzation, which hydroxy compound consists of an aromatic compound with at least two OH groups which directly, or via a methalene group, are linked to a carbon atom in the aromatic nucleus.