The CRATI Project: New Insights on the Consolidation of Salt Weathered Stone and the Case Study of San Domenico Church in Cosenza (South Calabria, Italy)

Michela Ricca,Silvestro A Ruffolo,Maurizio Licchelli,Natalia Rovella,Mauro F La Russa,Emilia Le Pera,Marco Malagodi,Maduka L Weththimuni,Luciana Randazzo,Andrea Macchia

doi:10.3390/coatings9050330

Abstract

This paper presents the results of a laboratory experimentation carried out on stone materials in the framework of the CRATI project (Knowledge and Restoration through Advanced Integrated Technologies) aimed at testing new products with consolidating properties by means of an integrated methodological approach. After the preliminary characterization of stone materials collected in the pilot site, the second stage of the activities within the project were focused on the formulation and testing of products for the conservation of the same materials against decay, especially salt crystallization, one of the most aggressive and common degrading processes. The San Domenico Church, located in the old town of Cosenza (Calabria, Southern Italy) has been chosen as the pilot site and for the in situ tests. Several specimens with the same features of the stone materials used in San Domenico church were collected from a historical quarry near the city of Cosenza. These specimens were treated and then artificially degraded by salt crystallization tests in order to evaluate their susceptibility to weathering intensity. Three different consolidating products were used; respectively, two commercial and another one formulated in laboratory: (a) a suspension of nanosilica (Nano Estel®); (b) a suspension of nanolime (CaLoSiL®), and (c) a suspension of nano calcium-hydroxide dispersed in isopropyl alcohol and then mixed with diammonium hydrogen phosphate. A systematic approach, including minero-petrographic, geochemical and physico-mechanical techniques, was applied to evaluate (a) the nature and main features of materials; (b) the efficacy of consolidating treatments, and (c) the resistance of treated stone to the salt crystallization processes. The tested products demonstrated a significant efficiency to consolidate and protect stone material samples, enhancing their resistance to salt crystallization. Thus, such a case history may be useful in order to plan appropriate restoration interventions that consider the interactions between the building stone and the protective/consolidating product.

Highlights

Introduction and Historical SettingThe conservation of weathered stones is an important topic in the field of cultural heritage and restoration activity, such that the correct choice of conservation strategy represents an essential objective for scientists working in this research area, to be applied to, and evaluate on a case by case basis.Consolidation treatments aim to prevent stone decay, decohesion phenomena and weathering forms
A consolidant product is used to improve the cohesion of weathered stones when serious decay patterns and in-depth cohesion loss are present in order to increase the mechanical strength of the rock [1,2,3,4]
After the preliminary characterization of stone materials collected in the pilot site through minero-petrographic and geochemical techniques, the second phase of activity was devoted to the formulation and testing of products for the church conservation

Summary

Introduction

Introduction and Historical SettingThe conservation of weathered stones is an important topic in the field of cultural heritage and restoration activity, such that the correct choice of conservation strategy represents an essential objective for scientists working in this research area, to be applied to, and evaluate on a case by case basis.Consolidation treatments aim to prevent stone decay, decohesion phenomena and weathering forms. The application of suitable products leads to a reduction of the stone’s susceptibility to various decay phenomena, and especially to soluble salt crystallization decay [5]. The latter is one of the most dangerous weathering agents in porous building materials that limit its durability, in limestone [6,7,8,9,10]. For this reason, the first step is to understand deeply this degradation process, in order to prevent or limit the damage. The experimentation of innovative consolidation products is required to identify those most appropriate, considering their compatibility with both the environment and the materials

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Results