First, C-S-H with Ca/Si = 1.34 and mean chain length (MCL) = 2.55 (Figure ) corresponds to a typical low Ca/Si C-S-H as might be synthesized from CaO and SiO 2 without the presence of portlandite . A C-S-H nanofoil model of 3-layer thickness with this Ca/Si and MCL results in a structure that has, in addition to Ca in the mainlayer, Ca occupying all vacant Q 2b sites. With only the mainlayer (69 % of all Ca sites) and bridging Ca site (31 % of all Ca sites), the Ca/Si ratio of 1.34 at MCL = 2.55 is achieved. No Ca adsorption at the surface is needed. As seen in Figure the expected Ca NMR spectrum has a clear peak at 33.5 ppm due to the prevalence of mainlayer Ca site and a formation of the left shoulder, due to the bridging Ca site with δ DFT = 46.84 ppm.