The theoretical study of Ca NMR spectrum of C-S-H here presented has the potential to further help elucidate the C-S-H structure particularly in answering the question, of whether all synthetic C-S-H, from various precipitation methods, are the same. Due to the distinct chemical shift of C-S-H Ca sites it should be possible to compare the Ca NMR spectra of the samples from different synthesis methods, and obtain an estimation of the proportion of the Ca sites. With this a further step in understanding the interlayer and surface structure of C-S-H could be possible.