Lime-diatomaceous earth cement pastes were fabricated at room temperature starting with a mixture of diatomaceous earth (DE), lime, and water. The cementing phase, associated with the pozzolanic reaction of the diatom skeletons with lime, was identified as calcium silicate hydrate (C-S-H) gel using X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The FTIR and NMR results revealed that the C-S-H gel is mainly composed of silica dreierketten in all lime pastes using three different types of DE.