Method for producing a foundry body, preferably a mould and/or core for a foundry piece, said method comprising at least the following successive steps: - preparing a granular mixture, comprising, in % weight with respect to the total weight of the mixture: a- at least 90%, preferably 96 to 99% by weight of grains, said grains being mainly composed of at least one mineral oxide, and at least 80% of said grains having a size from 10 to 3000 μm, b- 0.3 to 3%, preferably 0.6 to 1.5% by weight of at least one resin polycondensed with formaldehyde and/or its derivatives, the percentage being calculated in dry resin solids, c- 0.001 to 3%, preferably 0.005 to 1% by weight of at least one curing agent, the percentage being calculated in dry curing agent solids, d- 0.003 to 1%, preferably 0.01 to 0.15%, by weight of at least one formaldehyde scavenger compound, and f- 0.2 to 3%, preferably 0.7 to 2%, by weight of water; - placing said granular mixture in contact with at least one surface of a forming tool, and - blowing at least one gas stream into the granular mixture at a temperature of 50°C to 380°C, for a duration comprised from 1 to 300 seconds, in order to ensure at least partial curing of said mixture, Said method being characterized in that the polycondensed resin (component b -) of said mixture is modified: • Either by the presence of a component e- in the mixture, at a content from 0.003% to 1.5%, preferably from 0.15% to 1%, by weight with respect to the total weight of the mixture, of at least one resin chosen from the group consisting of tannins, natural polyphenols and lignins, • Or by the presence during its synthesis of a compound comprising at least one phenolic and/or polyphenolic unit, at a content from 1 to 30% by weight with respect to the total weight of the polycondensed resin. - preparing a granular mixture, comprising, in % weight with respect to the total weight of the mixture: a- at least 90%, preferably 96 to 99% by weight of grains, said grains being mainly composed of at least one mineral oxide, and at least 80% of said grains having a size from 10 to 3000 μm, b- 0.3 to 3%, preferably 0.6 to 1.5% by weight of at least one resin polycondensed with formaldehyde and/or its derivatives, the percentage being calculated in dry resin solids, c- 0.001 to 3%, preferably 0.005 to 1% by weight of at least one curing agent, the percentage being calculated in dry curing agent solids, d- 0.003 to 1%, preferably 0.01 to 0.15%, by weight of at least one formaldehyde scavenger compound, and f- 0.2 to 3%, preferably 0.7 to 2%, by weight of water; a- at least 90%, preferably 96 to 99% by weight of grains, said grains being mainly composed of at least one mineral oxide, and at least 80% of said grains having a size from 10 to 3000 μm, b- 0.3 to 3%, preferably 0.6 to 1.5% by weight of at least one resin polycondensed with formaldehyde and/or its derivatives, the percentage being calculated in dry resin solids, c- 0.001 to 3%, preferably 0.005 to 1% by weight of at least one curing agent, the percentage being calculated in dry curing agent solids, d- 0.003 to 1%, preferably 0.01 to 0.15%, by weight of at least one formaldehyde scavenger compound, and f- 0.2 to 3%, preferably 0.7 to 2%, by weight of water; - placing said granular mixture in contact with at least one surface of a forming tool, and - blowing at least one gas stream into the granular mixture at a temperature of 50°C to 380°C, for a duration comprised from 1 to 300 seconds, in order to ensure at least partial curing of said mixture, • Either by the presence of a component e- in the mixture, at a content from 0.003% to 1.5%, preferably from 0.15% to 1%, by weight with respect to the total weight of the mixture, of at least one resin chosen from the group consisting of tannins, natural polyphenols and lignins, • Or by the presence during its synthesis of a compound comprising at least one phenolic and/or polyphenolic unit, at a content from 1 to 30% by weight with respect to the total weight of the polycondensed resin.