the invention concerns a filtering wall designed for an expendable formwork comprising a lattice formed by assembling flexible warp and weft yarns , the lattice being stretched on an undeformable structure . the filtering wall is characterized in that some of the warp yarns are more resistant than other warp yarns , the lattice being stretched by traction solely exerted on the more resistant warp yarns and in that it comprises tension maintaining means for maintaining the tension associating the more resistant yarns with the undeformable structure , the tension maintaining means delimiting a larger mesh than the one resulting from the initial interlacing of the warp and weft yarns .