The invention relates to a method for the densification of a porous fibrous refractory substrate, comprising the formation of a solid matrix deposit. The inventive method is performed using a fluid composition containing a reactive fluid that is a precursor of the material of the solid deposit to be formed and an optional dilution fluid. The method is carried out at a temperature and pressure that enable the reactive fluid and/or the optional dilution fluid to be maintained in the supercritical state, while simultaneously and directly forming the solid matrix deposit. In this way, the length of the process can be reduced considerably in relation to standard CVI methods.