A novel approach to compatible and durable consolidation of limestone

In the field of stone conservation, consolidation is of paramount relevance and the most critical tasks required are durability and compatibility of the products to be applied with the original substrates. Due to the lack of conservation efficiency of a great variety of commercial polymers employed as stone preservatives, a novel approach for limestone consolidation has been pursued with the aim to identify suitable products for a compatible and durable treatment. Linear and branched calcium metallorganic compounds have been designed, synthesized and their potential as stone consolidants evaluated. They have been applied either on glassy substrate and on deteriorated marble specimens to study respectively the kinetic pathways leading to calcium carbonate and the induced variation of marble cohesion. Preliminary tests have been performed on calcium alkoxides and other inorganic products, i.e. ethyl silicate (TEOS), solution of Ba(OH)2, (NH4)2CO3 and alcoholic suspension of Ca(OH)2, to compare the consolidant efficiency. Physico-chemical measurements (?-FT-IR. FEG-ESEM-EDS, XRD) have been used to study the mechanism of CaCO3 formation, while stone cohesion was evaluated by ultrasonic velocity tests. The strengthening effects of Ca(OCH3)2 turned out to be comparable to traditional inorganic consolidants. Furthermore, calcium alkoxides are effective even in very low concentration as the impregnation occurs without pore saturation, thus ensuring the vapour permeability of the treated stone without the detrimental effects of coating cracking , as observed when TEOS is employed, or pore sealing produced by several organic polymers.