The "grey" of Brunelleschi and Michelangelo. Pietra Serena is a sandstone that defined the aesthetics of the Florentine Renaissance. Its unmistakable blue-grey color and extremely fine, homogeneous grain make it a perfect canvas for sculpture and the architectural modulation of interior spaces.
Belonging to the geological formation of the Macigno Toscano, Pietra Serena is a clastic sedimentary rock generated by ancient submarine turbidity currents. It is composed of very fine granules of quartz, feldspar, and flakes of mica (particularly biotite, responsible for the bluish coloration), held together by a natural clayey and calcareous cement. This isotropic composition gives it excellent workability: it can be cut, chiseled, and honed with great precision, allowing the creation of moldings, capitals, and columns with sharp and defined details.
While indoors Pietra Serena retains its beauty over the centuries (as Florentine churches demonstrate), outdoors it reveals its chemical-physical weakness. The clayey cement that binds the granules is hydrophilic and reacts very badly to atmospheric agents. Rainwater penetrates the pores by capillarity (3-5%); in case of thermal drops, the transition to ice (cryoclasty) increases the volume of water by 9%, causing a fatal internal tension. This phenomenon leads to the typical exfoliation or onion-skin flaking: the stone flakes off losing successive superficial layers, until it pulverizes.
Standards
European and international references applicable.
Physical properties
Usage environment
For outdoor use (e.g. paving or facade cornices) or in the restoration of degraded ashlars, treatment with Ethyl Silicate or siloxane water repellents is mandatory, which penetrate the porosity rebuilding the lost mineral bond and repelling liquid water while maintaining vapor breathability.