We have studied the formation of three-dimensional silicon alkoxide-based network resulting from an inorganic polycondensation based on hydrolysis and condensation reactions. Using mechanical spectroscopy, small-angle X-ray scattering, and penetration measurements, we have shown that viscoelastic and morphological properties of gelling soft matter systems can be modulated according to the nature of a catalyst by modifying the rate of the hydrolysis and condensation reactions. The description of the network build up in terms of a continuous transition between three viscoelastic states leads us to obtain new information on the viscoelastic properties determined up to now only at the sol-gel transition.