Abstract: The invention provides that a layer of hardened material is created on the surface of an underground passageway, in particular a sewer so as to restore its utility and the method used is to place a first lining tube in the sewer along its length, and then to evert a second tube of smaller diameter, along the sewer into the first tube. The method is to insert into the first tube a fluent mass against which the second tube is everted and the fluent mass comprises a hardenable material, typically a synthetic resin and a solid particulate material, typically even diameter beads, which serves to limit the thickness to which the mass can be compressed between the tubes whereby an even thickness layer of the fluent mass lying circumferentially of the sewer forms between the tubes, and this layer is held and is hardened either by force or naturally.