a 104 d 104 h or may be a relatively short member compared to its width e g 110 a 110 b 110 c or may be an intermediate length member e g 104 b 104 c or may be formed of multiple shorter member sections connected to form an elongate formwork member these sections may be bonded together such as by an adhesive or may be mechanically joined by one or more connectors or fasteners fig6 a and 6 b show a sectional view of two stages of an alternative form of the invention for creating a window or door opening compared to that shown in fig5 essentially the formwork members 122 b 122 c and the subsidiary panel 120 of fig5 are combined into one or more thick formwork members 132 a 132 b 132 c it will be appreciated that a single formwork member 132 of suitable dimensions to define the required opening measurements width and height could be used as previously described the formwork panel s u2018 keys u2019 into the inner facing material or other facing sheet or coating and a final finishing layer 129 may be applied fig6 a shows three formwork members keyed into the inner first face 124 of the inner facing material these formwork members are 150 mm thick compares with 100 mm thickness of the formwork members 122 a d the additional thickness helps to support the edges of a coating when applied to the formwork members 122 a 122 d adjacent to the opening to be formed and makes the door or window.