Considerable attention is often dedicated to ensure the tightness of the formwork when placing ready-mixed self-compacting concrete (SCC). These sealing actions lead to additional costs, making the self-compacting concrete solution more expensive than casting traditional vibrated concrete. This paper presents the results of an experimental research, regarding the required tightness of the joints between formwork panels when using SCC as non-fair faced, structural concrete. First, small scale tests are executed using artificial increase of the pressure exerted onto the tested SCC inside the formwork. In the second phase of this research, experiments are conducted on real scale formwork constructions (up to 6m of concrete height). A wide range of calibrated joint openings between the formwork panels are tested. During casting of the SCC the mortar loss through the gaps is visually observed. After removal of the formwork, the surface and corners of the hardened concrete elements are analysed. The acceptable gaps between the formwork panels can reach values of up to 7 mm and higher, without leading to honeycombing and/or too widely spread 'infected' zones on the concrete surface.