This graduation project is in cooperation with TU Delft, Tentech BV, Aectual and White Lioness technologies. It aims to investigate the feasibility of using recycled plastics as material for large-scale 3D printing with the 3D printer KamerMaker. In the meantime, a thickness distribution methodology is proposed for taking advantage of the flexibility of the 3D printing technology to optimise the printed structure, especially as moulds for casting concrete, to increase the structural efficiency. The content of the project contains laboratory tests, numerical modelling, design methodology and a case study.