Ceramic roof tiles are extremely common building materials that are subjected to the natural phenomenon of biodeterioration, which initially modifies the tile surface and ultimately causes its destruction. The bacterial diversity of the visible biofilm responsible for biodeterioration has been previously examined. In contrast, the early stages of tile colonization and pioneer biofilm growth on these surfaces have been poorly explored. To investigate these pioneering stages of bacterial tile colonization, we combined imagery and conventional culture-based approaches, as well as Illumina-based high-throughput sequencing methods to examine samples collected from unexposed new tiles and tiles that were subjected to few-months outdoor exposure. In all the samples, we observed a pioneering biofilm including a significant bacterial diversity, on both new materials and those subjected to slight exposure, with a total of 279 and 411 different OTUs detected, respectively. This pioneer diversity was dominated by Proteobacteria (more than 50% of the total bacterial diversity) and, at the genus level, by Sphingomonas and the genus 1174-901-12 related to the Beijerinckiaceae. Interestingly, the major patterns of the observed bacterial diversity remained similar between samples collected from unexposed and exposed tiles. Collectively, these data clearly indicate the need to focus on the pioneer colonizing bacteria that form the initial biofilm on building materials, which can subsequently lead to mature biofilm formation and visible biodeterioration.