X-ray diffraction patterns of synthetic C-S-H show a remarkable resemblance with the tobermorite 14 Å structure and can be fitted with its monoclinic B11b cell with a high accuracy . Although it is known from Si NMR that the C-S-H silicate chain structure is highly defective (missing bridging Q 2b sites) the resemblance of the X-ray diffraction pattern, including the position of its peaks, suggests very similar if not nearly identical ordering of the mainlayer.