Anhydrous silylation of vinyltrimethoxysilane (VTMS) onto silica and zirconia substrates was investigated experimentally to demonstrate and quantify the effects of surface water on multilayer silylation. Silylation coverage was controlled by the availability of surface water, which is consumed in multilayer silylation reactions. Silylation coverage increased with surface water coverage, reaching a maximum at approximately two monolayers of water. The subsequent decline in silylation coverage is attributed to the formation of bulk polysilanes and the decreased accessibility of the water-bearing surface to the hydrophobic VTMS molecules. Atomic force microscopy images revealed a nanometer-scale clusterlike surface morphology consistent with the formation of bonded polysilanes. The present study suggests that multilayered silylated surfaces can be prepared reproducibly. Such surfaces could prove useful in applications that require a high concentration of surface active groups such as in ceramic membrane modification, construction of biocompatible surfaces, and adhesion enhancement in polymer composites.