Rock petrophysics vs. performances of protective and consolidation treatments: the case of Monte Arzolo Sandstone

Abstract: The petrophysical characteristics of a building stone used in the city of Pavia, northern
Italy, are analysed in the light of stone conservation through the application of water repellent and
consolidant products. The research focuses on the modification of petrophysical properties as a
function of the applied products, and on the critical assessment of the performances of fluorinated
and siloxane resins as a function of the variable nature of the same lithotype. The studied material
is a calcareous sandstone (Mt Arzolo Sandstone), Late Miocene–Early Pliocene in age, extensively
employed as a building material during the 11th and 12th centuries. Experimental investigations
on samples from historic quarries were performed before and after application of
treatments: i.e. petrographical and fabric analyses; ultrasonic measurements; mercury porosimetry;
abrasion resistance measurements; contact angle measurements; capillary and low-pressure
water absorptions; water vapour permeability; and colour measurements. Two main lithotypes
of Mt Arzolo Sandstone were recognized according to their petrophysical features: the open
porosity being similar, differences exist concerning their fabric. These differences influence the
physical–mechanical properties of the material and consequently the performances of the
applied products. In particular, the difficulties in penetration of products when sandstone of
smaller pore size is treated can lead to a significant reduction of the overall performances,
which is more evident for products containing organic solvent with high molecular weight.