Travertine is a material formed by hot springs, the mineral-rich waters evaporate leaving behind deposits of calcium carbonate which solidifies to form travertine. Geologically very young, this stone is often deposited around vegetation which then decays leaving voids in the stone. These voids may be on the surface of the tile or can sometimes be just below the surface of the tile and can become exposed with use.

The surface voids may be filled as part of the finishing process, if any fill becomes dislodged or holes become exposed then a suitable resin-filler  can be used to rectify. Use pH neutral cleaners to avoid any damage to this acid-sensitive material.