Chemical analysis of historic lime mortars: role of sample preparation Radek Ševčík 1,a , Petr Šašek 1,b , Marta Pérez-Estébanez 1,c and Alberto Viani 1,d 1 Institute of Theoretical and Applied Mechanics ASCR, Centre of Excellence Telč, Batelovská 485- 486, 588 56 Telč, Czech Republic a sevcik@itam.cas.cz, b sasek@itam.cas.cz, c estebanez@itam.cas.cz, d viani@itam.cas.cz Keywords: Lime, mortars, calcite, acid digestion, Rietveld method. Abstract. The characterization of historic lime mortars is crucial for many cultural heritage conservation issues. In this work, the characterization of a historical lime mortar is described. Samples for chemical analysis were obtained after different milling times and using the RILEM acid digestion method on several replicates. Qualitative and quantitative determination of phases in the mortar and in the residues after acid attack and the potential presence of CaCO 3 polymorphs, were accomplished with X-ray powder diffraction. Results suggest that representativeness of the sample and the homogenisation, although not always achievable in conservation practice, are strongly affecting results. Introduction Lime mortars are important building materials produced and used by mankind as a binder in mortars for brickwork, stonework, rendering and plastering over centuries [1].The final properties of lime mortars are strongly influenced by the nanostructural and colloidal characteristics of lime, and by the extent of the carbonation process, that substantially contribute to their final strength. Carbonation process is the reaction between atmospheric CO 2 and Ca(OH) 2 in an aqueous medium, resulting in the formation of CaCO 3 [2]. In general, CaCO 3 occurs as three anhydrous crystalline polymorphs (calcite, aragonite, vaterite) and in two hydrated crystal forms ikaite (calcium carbonate hexahydrate) and calcium carbonate monohydrate [3]. In the recent years, the use of lime as repair material in the field of cultural heritage conservation has gained increasing interest. A widely shared approach is to match the repair material with the original. This keeps the conservation intervention to the minimum, provides some continuity with the past, and, most of all, will ensure that the repair material will age in a similar way as the original. Changes are usually made only where the existing materials have been shown to be inappropriate. In this light, it’s clear that the choice of the right repair mortar must be based on sound information about the state of the original material. Many efforts have been devoted in the last years to establish protocols for the analysis of historic mortars. This drive toward standardization of analytical procedures in order to allow the comparison of results between laboratories, led to the integration of multiple analytical methods [4-5]. Acid digestion followed by wet chemical analysis is still considered an essential step of this process. However, several different procedures for the determination of analytes are described in the literature [6]. They differ for several aspects, such as the type of acids employed, their concentration, the sample to acid ratio and the methodology for powder milling before acid attack. Owing to the complexity of these materials, it is of relevance to investigate how results can be affected by aspects such as sample preparation and sample nature. The first important step in mortar analysis is to ensure the representativeness of the sample. This aspect is often overlooked, in part because for objects of relevance for cultural heritage, the conservator specialist is often forced to collect a limited amount of sample. In strongly heterogeneous samples as mortars, this may lead to misleading if not completely unreliable results. In this work, results of the analysis of an historic mortar are reported. The mortar was studied with petrographic microscope and X-ray powder diffraction (XRPD). RILEM acid digestion method [5] was chosen for the preparation of liquid samples to be analysed with inductively Advanced Materials Research Submitted: 2014-11-13 ISSN: 1662-8985, Vol. 1100, pp 17-20 Accepted: 2014-12-21 doi:10.4028/www.scientific.net/AMR.1100.17 Online: 2015-04-29 © 2015 Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 132.239.1.230, University of California, San Diego UCSD, La Jolla, USA-15/04/16,12:23:32)