FORMWORK FOR USE IN CONCRETING SQUARE HOLES FOR DOORS AND WINDOWS

The invention relates to a cardboard formwork (200) for use in a concrete wall panel (100) which, during concrete casting, is embedded in concrete to form a square hole for doors (101) and/or windows (102), and/or other building-related components (103) , inside the concrete wall panel. The cardboard formwork comprises a square formwork formed by folding one or more cardboard sandwich elements made from recyclable cardboard, in particular a formwork having a corresponding chamfer (400) with a sloping edge projecting outwards from the outer edge and along the outer edges. The production reduces production time, improves the working environment due to lower weight and is more environmentally friendly because cardboard can usually be recycled more easily than wood or metal.