Please cite this article in press as: G. Borsoi, et al., Understanding the transport of nanolime consolidants within Maastricht limestone, Journal of Cultural Heritage (2015), http://dx.doi.org/10.1016/j.culher.2015.07.014 ARTICLE IN PRESS G Model CULHER-2983; No. of Pages 8 Journal of Cultural Heritage xxx (2015) xxx–xxx Available online at ScienceDirect www.sciencedirect.com Original article Understanding the transport of nanolime consolidants within Maastricht limestone Giovanni Borsoi a,∗ , Barbara Lubelli a,b , Rob van Hees a,b , Rosário Veiga c , António Santos Silva d a Heritage & Architecture Section, Faculty of Architecture, TU Delft, Julianalaan 134, 2628 BL Delft, The Netherlands b Division of Structural Reliability, TNO, Van Mourik Broekmanweg 6, 2628 XE, Delft, The Netherlands c Building Division, LNEC, Av. do Brasil 101, 1700-066 Lisbon, Portugal d Materials Division, LNEC, Av. do Brasil 101, 1700-066 Lisbon, Portugal a r t i c l e i n f o Article history: Received 7 March 2015 Accepted 21 July 2015 Available online xxx Keywords: Nanolime Consolidation products Transport Penetration depth Limestone a b s t r a c t Novel nanomaterials, such as nanosilica or nano-titanium oxide, have been developed in the last decade for the conservation of the built heritage. Among nanomaterials, nanolimes have acquired a considerable relevance due to their potentialities as consolidant product. The so-called nanolimes, colloidal disper- sions of calcium hydroxide nanoparticles in alcohols, have been successfully applied as pre-consolidants on frescos and paper, and their use has later been extended to plasters, renders and stone. Nanolimes have better potentialities compared to conventional inorganic consolidants based on limewater (e.g. faster carbonation rate and higher calcium hydroxide concentration). Moreover, nanolimes are consid- ered more compatible with CaCO 3 -based substrates than alkoxysilanes (e.g. TEOS), the most widely used consolidant products. Nanolimes can guarantee the recovery of the superficial cohesion of degraded materials. However, when a mass consolidation is required, like in the case of decayed stone, nanolimes show some limitations. One of the problems is caused by nanolime accumulation at or just beneath the surface of the treated material. In order to solve this problem, the transport mechanism of nanolime within porous materials, as stone or renders, should first be better understood. Commercial nanolimes were applied on Maastricht limestone, a high-porosity yellowish limestone, used in the Netherlands and Belgium as traditional building material. The absorption and drying behaviour of nanolime in this lime- stone was measured and nanolime deposition in the stone was studied by optical and scanning electron microscopy. The results show that nanolime transport is strictly related to the properties of the solvent. The alcoholic solvent guarantees a stable dispersion that penetrates in depth in the material, but is par- tially back-transported to surface. The high volatility of the solvent and the high stability of the dispersion favour the partial back-migration of lime nanoparticles to the surface during drying. © 2015 Elsevier Masson SAS. All rights reserved. 1. Introduction Calcareous materials such as limestone have demonstrated over the centuries to be durable building materials. However, if exposed to the action of atmospheric agents, these materials may suf- fer several degradation processes (e.g. salt crystallization, frost action, biological growth) leading to surface decay. Decay patterns showing in the form of loss of cohesion (e.g. powdering, sanding, ∗ Corresponding author. Tel.: +31 0 64 84 62 313; fax: +31 0 15 27 84 094. E-mail addresses: G.Borsoi@tudelft.nl (G. Borsoi), B.Lubelli@tudelft.nl (B. Lubelli), rob.vanhees@tno.nl (R. van Hees), rveiga@lnec.pt (R. Veiga), ssilva@lnec.pt (A.S. Silva). chalking) can be recovered through the application of consolidant products. A consolidation treatment should fulfil three main require- ments: effectiveness (i.e. improvement of the mechanical strength), compatibility (with the treated substrate) and durability (resis- tance to different damage mechanisms) [1–3]. In fact, the concept of compatibility of an intervention has nowadays replaced that of reversibility. Products used for conservation issues should be com- patible, from the chemical, mechanical, physical and aesthetical point of view, with the substrate on which they are applied [3]. Organic consolidants such as acrylic and epoxy resins have generally a low durability and compatibility when applied on cal- careous substrates [1,2,4]. Tetraethyl orthosilicate (TEOS), often referred to as ethyl silicate or silicic acid ester, is at present the most widely used consolidants for limestone, mainly because of the http://dx.doi.org/10.1016/j.culher.2015.07.014 1296-2074/© 2015 Elsevier Masson SAS. All rights reserved.