Nine unique C-S-H bulk structures containing 1 or 2 defective tobermorite 14 Å unit cells were generated with the brick model methodology from Kunhi Mohamed et al . The typical C-S-H defects (missing Q 2b silicate, addition of Ca 2+ and OH -ions in the interlayer) were accounted for . Through these defects C-S-H structures with Ca/Si ratios between 1.4 and 1.8 were generated. Afterwards, the water and ions in the C-S-H interlayer of the unique structures were randomly shuffled. Through this 77 different starting configurations were obtained. Further, the interlayer space of 3 unique structures was expanded through addition of water molecules to create two C-S-H (001) basal surfaces. The water slab between the surfaces was approximately 2 nm. Again, the water and ions were randomly shuffled to create 32 starting configurations for the C-S-H surface. Finally, 16 starting configurations with one Ca 2+ and two OH -ions in a water box were generated. All structures are part of the supplementary information (SI) section.