Renders and plasters have significant functions in buildings. Their functionality is closely related to their properties, which depend on the mortar itself, the application technology, the interaction with the environment and the substrate. There are many basic characteristics that influence the performance of renders and plasters; however, many of them are interrelated, thus the set of characteristics to be determined in each case is different, depending on the specific at each time use. These characteristics, their interrelations and the grouping of them are discussed and schematically described in the first and introductory section. Three groups are considered for renders and plasters: properties of fresh mortars; properties related to the hygric behaviour; and the mechanical behaviour. The properties of lime-based mortars measured in laboratory are highly affected by factors, such as: need of long time for development of representative values for prediction of their life-time behaviour, proper climatic conditions adequate for carbonation or/and hydration, sensitivity to the suction of water by the substrate. The last two factors—environment and substrate—have an important role for rendering and plastering with lime-based mortars, since both their exposed surfaces and the substrate areas they cover are large. Due to those specificities, the current test methods that have been mainly developed for cement-based mortars are not always fitted to characterize lime-based mortars, and in particular to assess lime-based renders and plasters. In section two the main characteristics and current standardized test methods are discussed based on experience in using them. Furthermore, needs of improvement are identified and changes are proposed, or, in some cases, new methods are outlined. Some of the most significant changes proposed are the possibility, as an option, to apply the mortar on a porous substrate, instead of moulding specimens in metallic moulds, together with modifications on curing conditions and times of mixing and testing. Additionally, test methods developed at laboratory to evaluate the cracking tendency due to restrained shrinkage and to determine the modulus of elasticity of under checking mortars are proposed, as well as alternative test methods for adhesion. In the case of testing other properties, smaller changes are proposed, in order for the standardized test methods to be adapted to the particularities of lime-based renders and plasters. As conclusions, in the third section, a synthesis of the proposed changes and complementary tests has been made in formulated tables, that could be considered as a first approach of adapted requirements for better performance of lime-based mortars for renders and plasters.

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For conservation interventions of historic masonry generally lime-based mortars such as pure air lime mortars, lime-pozzolan mortars, natural hydraulic lime mortars and ternary mortars (lime-pozzolan-cement) are used. The main reason is that their hygric and mechanical (strength and ductility) performance are easy to adapt to most existing historic masonry (compatibility requirements). Although the basic appropriateness of lime-based mortars for restoration is undisputed, there are also some limitations in the application of these mortars. In this report a review is given of the theoretical backgrounds and further of laboratory research developments in the field of lime-based binders and mortars over the past decades. Furthermore, practical experiences in positive and negative sense (damage cases) are elaborated. Drawbacks and points of attention are being dealt with, which are essential for a durable application of lime-based mortars for the conservation of historic masonry. In general, it is concluded that points of attention should be addressed through a thorough evaluation of their potential and through testing of their suitability. For these mortars, even more than for modern cement-based mortars, specifically, environmental exposure conditions and application conditions should be considered.

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Due to an unfortunate turn of events, the article title was only partly given in the article next to the fact that the list of TC members had accidently been left out. Please find in this erratum the correct article title and the list of TC members. Both should be considered as part of the final version by the reader.@en

The potentialities of nanomaterials for applica- tion in the field of conservation have been widely investi- gated in the last two decades. Among nanomaterials, nanolimes, i.e., dispersions of lime nanoparticles in alco- hols are promising consolidating products for calcareous materials. Nanolimes are effective in recovering the very superficial loss of cohesion of decayed materials, but they do not always provide sufficient mass consolidation. This limitation is mainly related to the deposition of the nanoparticles nearby the surface of the material. Experi- mental research has been set up with the aim of improving the in-depth deposition of lime nanoparticles. Previous research by the authors has shown that nanolime deposition within a substrate can be controlled by adapting the nanolimes properties (kinetic stability and evaporation rate) to the moisture transport behavior of the substrate. Nanolime properties can be modified by the use of different solvents. In this research, nanolime dispersions have been further optimized for application on Maastricht limestone, a coarse porous limestone. Firstly, nanolimes were syn- thesized and dispersed in ethanol and/or water, both pure and mixed in different percentages. Subsequently, based on the kinetic stability of the nanolime dispersions, the most promising solvent mixtures were selected and applied on the limestone. The deposition of lime nanoparticles within the limestone was studied by phenolphthalein test, optical microscopy and scanning electron microscopy. The results confirm that nanolime dispersed in a mixture of ethanol (95 %) and water (5 %) can guarantee a better nanoparti- cles in-depth deposition within coarse porous substrates, when compared to dispersions in pure ethanol.@en

The paper addresses the consolidation of plasters and renders showing loss of cohesion, with the use of a treatment with a liquid consolidating product aiming to reach a depth of several mm up to several cm. The main aim of the paper is offering a guideline on how to choose a consolidant, suitable and compatible
for the mortar type and its condition, and how to assess the performance of a consolidation treatment.@en