Abstract: The invention concerns a method of providing a seal within a pipe or aperture in a vessel and preventing fluid flow therethrough, the method comprising: (a) providing a non-porous, expandable, flexible container within said pipe or aperture; (b) introducing an expandable polymeric material into said container so as to expand said container, thereby forcing said container to fill the cross-sectional area of said pipe or aperture and displacing any fluid in said pipe or aperture in order to provide an engineered blockage within said pipe or aperture; (c) applying a bonding resin between the external surfaces of said container and the internal surfaces of the walls of said pipe or aperture; and (d) curing said expandable polymeric material and bonding resin so as to bond the expanded container to the pipe or aperture and create a seal between the outer surfaces of said container and the internal surfaces of the walls of said pipe or aperture.