Abstract: A molding system for molding large diameter chimney liners of fibreglass reinforced plastic (FRP) utilizes a vertically oriented cylindrical mold for use in combination with a working platform mounted on a vertical ram. The mold is of modular construction, having a plurality of axially spaced-apart spiders, each spider being segmented into a plurality of adjoining tri-angulated segments to form a polygon, to the outer sides of which are attached chordal segments to complete the circular form of the spider. Vertically axially extending ribs interconnect the spiders, with a flexible skin being applied thereabout. The provision of expansion means on the spiders increases the diameter of the mold to its working diameter, so that, upon completion of molding a liner, the action of the spider expansion means is reversed, causing contraction of the mold sufficient to facilitate ready axial separation of the mold and liner.