For improving permeability of a metallurgical vessel bottom provided with permeable refractory elements for controlled injection of a stirring fluid into a molten metal bath, the metallurgical vessel is emptied of its contents, a castable composed of a refractory material compatible with the refractory material of the bottom is deposited in the bottom and spread over the latter, and the castable is left to dry and set, while maintaining in the permeable refractory elements a sufficient pressure to provide a permanent flow of a stirring fluid. A hydraulic magnesian refractory castable used in this method has a content of water of substantially between 8 and 10% by weight.