Sandstone sedimentary rock typical of Florentine Renaissance architecture. Made up of grains of quartz, feldspar and mica bound by a clayey-calcareous cement. Elegant, homogeneous and easy to work, but structurally sensitive to the action of water and frost in outdoor environments.
The degradation of Pietra Serena outdoors. Capillary porosity allows water entry; the cryoclastic expansion of ice breaks the clay matrix causing flaking.
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.
European and international references applicable.
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.
The classic Renaissance use: blue-grey chromatic contrast against white lime plasters.
PRC.29 · Open the processHoned large-format slabs, historically used for churches, museums, and stately palaces.
PRC.24 · Open the processOutdoor use (selecting harder quarry banks, like "Pietra Forte") at very high thickness.
PRC.24 · Open the processReplacement (stitch-unpatch) of historical pietra serena ashlars irretrievably degraded by exfoliation.
PRC.29 · Open the processThe durability of a stone on a facade depends on its porous structure. Pietra Serena has "bad porosity" (capillary micropores that retain water), making it extremely vulnerable to winter freeze cycles if left exposed to the elements without protective siloxane treatments.
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