This recommendation is devoted to testing the resistance of natural stone and fired-clay brick units against salt crystallization. The procedure was developed by the RILEM TC 271-ASC to evaluate the durability of porous building materials against salt crystallization through a laboratory method that allows for accelerated testing without compromising the reliability of the results. The new procedure is designed to replicate salt damage caused by crystallization near the surface of materials as a result of capillary transport and evaporation. A new approach is proposed that considers the presence of two stages in the salt crystallization test. In the first, the accumulation stage, salts gradually accumulate on or near the surface of the material due to evaporation. In the second, the propagation stage, damage initiates and develops due to changes in moisture content and relative humidity that trigger salt dissolution and crystallization cycles. To achieve this, two types of salt were tested, namely sodium chloride and sodium sulphate, with each salt tested separately. A methodology for assessing the salt-induced damage is proposed, which includes visual and photographical observations and measurement of material loss. The procedure has been preliminarily validated in round robin tests.

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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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Historic Structures are commonly coated with mortar layers (plasters, renders, flooring) for protection and decoration. These well finished architectural stratigraphic surfaces often suffer from deterioration, such as lack of adhesion or detachment between support and mortar layers and even between mortar layers. Grouting and filling voids between delaminated layers can be an effective intervention if the layers are compact. This paper deals with aspects pertinent to the selection, design and implementation of a grout for the in situ stabilization and preservation of historic architectural surfaces. It presents the methodological approach, in accordance with the conservation principles, including sections on diagnosis, study and assessment of the deterioration phenomena, definition of grout requirements, selection of proper ingredients for custom-made or commercial grouts, as well as making and testing trial mixes, field testing and Assessment of the effectiveness of grouting. The aim of this paper, that is elaborated in the frame of RILEM TC 243 SGM, is to serve as a guide for users of lime-based grouts for the reattachment and reinstatement of historical architectural surfaces.

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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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Het blussen van een brand gaat gepaard met een grote hoeveelheid water die in het metselwerk van een gebouw binnendringt; daarnaast duurt het vaak ook nog lange tijd voor een gebouw weer waterdicht kan worden gemaakt. Dit kan een hoog vochtgehalte in de muren veroorzaken, met alle daaraan verbonden problemen, zoals zouttransport, zout- en vorstschade en biologische groei. In dit artikel wordt de casus van de Neo-classicistische Elleboogkerk te Amersfoort besproken, waarvan de kapconstructie in 2007 door een brand werd verwoest. Naast directe schade door de brand aan het gebouw en de daarin aanwezige museale collectie, ontstond er ook vervolgschade als gevolg van vocht. Onderzoek toonde aan dat een hoog vochtgehalte in de muren, in de nasleep van de brand, de oorzaak is geweest van het loskomen van het nieuwe pleisterwerk, binnen enkele weken nadat dit was aangebracht. Daarnaast maakte het onderzoek het mogelijk om, op basis van het gemeten zoutgehalte in de muur, het risico voor het verder ontstaan van schade in te schatten en advies te geven over het wel of niet vervangen van de (nog) niet beschadigde delen van het renovatiepleisterwerk.@en

Compatibility of repair materials in conservation is a widely desired goal, but difficult to achieve. In this research, the compatibility of four commercial stone repair mortars, commonly used in conservation practice in the Netherlands and neighbouring countries, is discussed. In order to do so, they have been characterized in laboratory. The composition of the repair mortars, their content of soluble salts, porosity and pore size distribution, hygric dilation and flexural and compressive strength were measured. The effect of curing was assessed by comparing specimens cured in laboratory and under outdoor conditions. The effect of 3 years outdoor exposure on the curing and weathering of the mortars was evaluated. The results show that the composition of the selected mortars varies significantly, even though, based on their technical information sheets, they appeared to be similar. Consequently, their moisture transport properties differ significantly. As expected, both the type of binder and the porosity were shown to affect the mechanical properties of the mortar: the mortar based on an inorganic polymer binder showed the highest mechanical strength; the most porous, lime- or lime-cement-based mortars, showed the lowest mechanical strength. Based on compatibility criteria defined in literature and the results obtained in this research, an attempt was made to assess the technical compatibility of the selected mortars with building stones commonly used in the Netherlands. It was found that some requirements are hard to be fulfilled and not all requirements can be fulfilled at the same time. Besides, technical sheets of commercial mortars are often incomplete; therefore repair mortars can hardly be selected based only on the properties reported by the producers.

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In the Netherlands a program for the enhancement of quality in the restoration of monumental buildings is presently carried out, stimulated by national authorities and coordinated by the foundation ERM. Guidelines are issued by the branches involved, from architects to masons, under guidance of an experts’ committee, to perform interventions on monuments and assess them. The aim of this paper is to discuss the contributions to the program offered by different actors active in the field of conservation, the existing synergies and the potential of using a common language and approach. These are needed to facilitate communication and exchange knowledge. The use of the terminology of MDCS (Monument Diagnosis and Conservation System) can help create a community of stakeholders. Sharing the damage terminology and methodology can help achieving a clear and systematic assessment of damage and its causes. It can further improve the communication among all stakeholders, including owners and laymen, stimulating cooperation, and can allow monitoring of damage and interventions.@en

Before starting any interventions related to the maintenance or restoration of a monument, a thorough investigation is necessary, aiming to assess damage to materials and structures and to obtain a well-supported diagnosis. This paper is based on a keynote lecture given in Leuven at the WTA-Precomos Conference on Preventive Conservation in April 2019; it discusses the importance of the use of so called damage atlases and presents the possibilities of using MDCS, the Monument Diagnosis and Conservation System, for diagnosis and monitoring. Originally created in 1995 within an EU project, MDCS has been developed into an online tool supported by the Cultural Heritage Agency of the Netherlands, TNO (Netherlands Organisation for Applied Scientific Research), and the Faculty of Architecture of Delft University of Technology.MDCS includes Damage Atlases allowing a uniform identification of the damage found. They form the base for making hypotheses on damage mechanisms and for performing visual monitoring. Apart from the use by professionals, visual monitoring can also be performed by owners, which encourages their active participation in preventive conservation. The Damage Atlases are being used by several Provincial Monumentenwacht Organisations in The Netherlands to enhance uniformity and quality of Monumentenwacht activities on preventive conservation. The system is also used to support the Dutch Governmental Programme on Professionalism, aiming at improving restoration quality, through implementation in the guidelines of the Foundation ERM.In the work of the WTA working group on damage monitoring, the option for visual monitoring will be proposed and used.@en

Weathering of porous building materials caused by the crystallization of soluble salts is a ubiquitous problem in the built cultural heritage. Especially lime-based mortars are susceptible to salt decay, due to both their bimodal pore size distribution and low mechanical strength. The addition of crystallization modifiers to mortars during mixing may confer them an improved resistance to salt decay. In this research, lime-based mortars additivated with ferrocyanide or borax (modifiers for sodium chloride and sodium sulfate, respectively) were prepared. An accelerated salt crystallization test was carried out to assess the effect of the modifiers on the salt resistance of the mortars. The development of damage was assessed by visual and photographical observations and by quantifying the salt and material loss. At the end of the test, SEM observations were performed on the surface and cross-section of the specimens, to study the effect of the modifiers on the crystallization habit of the salts. The ferrocyanide and borax additivated mortars showed a considerably improved durability with respect to salt crystallization damage. Both modifiers altered the growth morphology of the salt crystals inside the pores of the mortars.

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The Rietveld Schröder House is not only an icon of Dutch architecture, but also a museum welcoming about 18,000 visitors each year. The unusual experimental character of the construction and the fact that the house is open to the public
can be expected to affect the indoor climate and to pose some risks for the conservation of the building and the furniture. In order to assess possible risks related to the indoor climate and, if necessary, take measures, a monitoring of the indoor climate was carried out in 2017.@en

Salt crystallization damage in porous building materials is a widespread phenomenon. Several solutions to prevent, or mitigate, salt damage in building materials, prolonging thereby their service-life have been proposed. One of the latest approaches is the use of crystallization modifiers, aiming at reducing the crystallization pressure and/or favouring the crystallization of salts at the surface (efflorescence) instead of in the pores of the materials (crypto-florescence). This paper summarizes the working mechanisms of crystallization modifiers and critically reviews the available literature on their use in building materials; finally, it provides an outlook on the potentials of modifiers for the mitigation of salt crystallization damage in building materials.

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Surface repair mortars are used for the compensation, or repair, of lost portions of surface materials in historic masonry buildings. It is recommended that their design and application should be performed in a wider context of conservation values related decision making, to prioritise preservation of original fabric, authenticity of approach and maintenance of integrity, and not just on technical principles alone. However, a technical context for their design does exist, that requires understanding of the properties of the substrate that they will be applied onto, and adherence to minimum aesthetic (colour and texture) requirements. The principles of physical, mechanical and chemical compatibility of repair apply and the attributes of the repair mortar should be carefully matched to the substrate alongside a sacrificial behaviour (not more durable than the material being replaced). Guidance is given on the design, application and the functional requirements that must be met when using surface repair mortars.

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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

Steenreparatiemortels zijn mortels die in de conserveringspraktijk worden gebruikt om ontbrekende delen van baksteen of natuursteen in metselwerk of beeldhouwwerk aan te vullen. In de Nederlandse conserveringspraktijk worden steenreparatiemortels regelmatig gebruikt met wisselende resultaten, zowel qua compatibiliteit met het bestaande als qua (technische) duurzaamheid van de reparatiemortel zelf. Naast zelf samengestelde mortels zijn de laatste decennia ook verschillende geprefabriceerde steenreparatiemortels beschikbaar. De ruime keuze en de vaak schaarse informatie over mortelsamenstelling, -eigenschappen en -gedrag maken het moeilijk voor de gebruiker om een geschikte mortel te kiezen.
Dit artikel beschrijft de resultaten van een nog lopend onderzoek opgezet binnen het samenwerkingsverband MonumentenKennis (TNO, TU Delft, RCE) met als uiteindelijke doel criteria te formulieren voor de keuze van een steenreparatiemortel in de praktijk. Als eerste worden eisen aan steenreparatiemortels uit de literatuur besproken. Op basis van de uitkomsten van een laboratoriumonderzoek, interviews met experts en bezoeken aan case studies worden aangepaste keuzecriteria voorgesteld. Daarnaast worden suggesties gegeven hoe de samenstelling van een mortel aangepast kan worden om aan de gestelde eisen te voldoen.@en

Optrekkend vocht is een vaak voorkomend fenomeen in gebouwen. Vooral oude gebouwen die geen waterkerende laag (zoals bijvoorbeeld een trasraam) hebben, lijden aan dit probleem. De relevantie van optrekkend vocht blijkt ook uit het grote aanbod van producten voor het bestrijden van dit probleem. Het grote, gevarieerde aanbod en de beperkte literatuur over de effectiviteit van de bestrijdingsmethoden maken het moeilijk voor mensen werkzaam in de praktijk om een keuze te maken tussen de verschillende methoden.
Binnen het project EMERISDA, gefinancierd door het Europese Joint Program Initiative Cultural Heritage (JPI-CH), is onderzoek uitgevoerd naar de effectiviteit van de verschillende methoden met als uiteindelijke doel een beslissingssysteem te ontwikkelen ter ondersteuning van de praktijk.
Het onderzoek bestond uit literatuuronderzoek, een online enquête om de tevredenheid van de gebruiker (gebouweigenaren en instanties werkzaam in de conservering van cultureel erfgoed) te meten en experimenteel onderzoek in het laboratorium en in situ (aan schaalmodellen en aan gebouwen). De resultaten van het project zijn samengebracht in een digitaal beslissingssysteem. Dit systeem is ontwikkeld om gebruikers te ondersteunen in het vaststellen van de aanwezigheid van optrekkend vocht in gebouwen en in het kiezen van een geschikte interventie.@en

The treatment of rising damp is an important issue when dealing with the conservation and restoration of historic buildings. The most effective solutions for the problem of rising damp are usually very ‘invasive’: depending on the method, there might be a substantial loss of authentic materials, the intervention may have a significant impact on the stability of the construction, there could be a mild to very important visual impact, and the intervention might be irreversible. An efficient treatment for rising damp, without these disadvantages, would therefore be more then welcome. Several companies offer nowadays such a solution, in the form of so-called ‘electrokinetic’ methods. Within the research project EMERISDA (www.emerisda.eu) (Effectiveness of Methods against Rising Damp), on-site measurements have been carried out on more sites, in order to evaluate their effectiveness. On one of the sites, the effectiveness of such an electrokinetic method has been compared to more conventional injections of water repellent agents.@en

Additivating mortars with crystallization modifiers is a novel approach to mitigate salt crystallization damage in historic masonry. Once verified the effectiveness of crystallization modifiers in bulk solution, the next step consists in verifying whether: (i) modifiers are still effective when mixed in mortar and going through the carbonation process and (ii) modifiers alter any mortar properties which might limit their application. This research addresses these issues for sodium ferrocyanide and borax, modifiers for sodium chloride, and sodium sulfate, respectively. Several experimental techniques have been applied to elucidate these questions. The results show that the selected modifiers are still able to alter the salt crystallization after going through the carbonation process of the mortar. Besides, no major effects of the modifiers on the fresh and hardened mortar properties were observed. It can therefore be concluded that there are no restraints for the future use of these crystallization modifiers in restoration mortars.@en

Naar aanleiding van het historisch georiënteerde onderzoek naar oppervlaktebehandelingen (Nijland & Quist 2018) en het onderzoek naar het hervoegen van gehydrofobeerd metselwerk, beide uitgevoerd binnen de samenwerking tussen TNO, RCE en TU Delft in MonumentenKennis, ontstond het idee om aan de hand van een aantal casussen te kijken naar de duurzaamheid van hydrofoberingen. Voor de keuze van de casussen is teruggegrepen op twee onderzoeken/publicaties uit de jaren ’90 van de vorige eeuw waarin de prestatie van hydrofoberingen werd onderzocht (Van Hees & Koek 1994, Van Hees et al. 1998). Een aantal objecten dat in deze studies is onderzocht is in juni 2018 opnieuw bezocht en bij een deel van deze objecten zijn in november 2018 Karstenbuismetingen verricht om de waterabsorptie van de (bak)steen en het voegwerk te meten.@en