Manufacturing method for a fibrous preform of a composite material part, the preform being obtained by: - forming a fibrous texture from refractory ceramic fibres, - shaping the fibrous texture in a mould cavity present in an injection tool, - injecting a slurry containing a refractory ceramic particle powder into the fibrous texture present in the mould cavity, - draining the liquid from the slurry that passed through the fibrous texture and retaining the refractory ceramic particle powder inside said texture so as to obtain a fibrous preform loaded with refractory ceramic particles, - first demoulding of the fibrous preform, characterized in that the method also comprises, after the first demoulding of the fibrous preform, the following steps: - immersing the demoulded fibrous preform in a bath of a liquid suitable for decompacting the refractory ceramic particles present in the fibrous preform, - shaping the wet fibrous preform in a mould cavity present in an injection tool, - eliminating the liquid present in the fibrous preform, - additionally injecting a slurry containing a refractory ceramic particle powder into the fibrous preform present in the mould cavity, - draining the liquid from the slurry that passed through the fibrous preform and retaining the refractory ceramic particle powder inside said texture so as to obtain a fibrous preform loaded with refractory ceramic particles, - second demoulding of the fibrous preform. - forming a fibrous texture from refractory ceramic fibres, - shaping the fibrous texture in a mould cavity present in an injection tool, - injecting a slurry containing a refractory ceramic particle powder into the fibrous texture present in the mould cavity, - draining the liquid from the slurry that passed through the fibrous texture and retaining the refractory ceramic particle powder inside said texture so as to obtain a fibrous preform loaded with refractory ceramic particles, - first demoulding of the fibrous preform, characterized in that the method also comprises, after the first demoulding of the fibrous preform, the following steps: - immersing the demoulded fibrous preform in a bath of a liquid suitable for decompacting the refractory ceramic particles present in the fibrous preform, - shaping the wet fibrous preform in a mould cavity present in an injection tool, - eliminating the liquid present in the fibrous preform, - additionally injecting a slurry containing a refractory ceramic particle powder into the fibrous preform present in the mould cavity, - draining the liquid from the slurry that passed through the fibrous preform and retaining the refractory ceramic particle powder inside said texture so as to obtain a fibrous preform loaded with refractory ceramic particles, - second demoulding of the fibrous preform. - immersing the demoulded fibrous preform in a bath of a liquid suitable for decompacting the refractory ceramic particles present in the fibrous preform, - shaping the wet fibrous preform in a mould cavity present in an injection tool, - eliminating the liquid present in the fibrous preform, - additionally injecting a slurry containing a refractory ceramic particle powder into the fibrous preform present in the mould cavity, - draining the liquid from the slurry that passed through the fibrous preform and retaining the refractory ceramic particle powder inside said texture so as to obtain a fibrous preform loaded with refractory ceramic particles, - second demoulding of the fibrous preform.