R.P.J. van Hees

Characterisation and damage analysis of old mortars

The scope of Rilem Committee TC167-COM is the characterisation of old mortars, with respect to their repair. For damage analysis of historic buildings, the characterisation of the old mortars may represent an essential part of the investigations. This statement can also be inverted, keeping in mind the scope of the committee and more specifically the second part ‘with respect to their repair’. It is essential to have knowledge of the condition of the old mortar and of the causes of any decay that has occurred (VAN HEES et al., 2000). The aim of this article is to underline the importance of knowledge on the factors that influence the way in which degradation of materials- and especially mortars in monuments - occurs. The most common forms of degradation of mortar in monuments, as well as the type of investigation, which is necessary to understand the cause of the damage, are described. On the basis of the assessed decay form and decay process, the most adequate repair method and the most suitable repair mortar can be chosen. The diagnosis of the damage is very often forgotten in practice, even though this is a fundamental step to guarantee a compatible and durable restoration. Such negligence can lead to major incompatibility problems in the case of repair mortar application. The approach discussed in this document can result in a better understanding of the causes of incompatibility and in guidelines for compatible repair mortars, based on the specific conditions of the individual monument. This article describes the approach, as proposed by Rilem TC167-COM .

Rilem TC 203-RHM: repair mortars for historic masonry. Performance requirements for renders and plasters

This article gives a summary of functional and performance requirements for renders and plasters for historic masonry (design, execution and maintenance). Specific attention has been paid to degradation effects, such as caused by salt crystallization and freeze–thaw cycling. Traditional as well as designed prefab mortars are considered for repair intervention.

Replacement of Eocene white sandy limestone in historical buildings: over 100 years of practice in the Netherlands

This paper discusses the replacement of white sandy limestone (Gobertange and Lede or Balegem) in the Netherlands in (successive) restorations from the mid-19th century onwards. White sandy limestone, transported from the southern part of the Low Countries (now Belgium), was extensively used in the northwestern part of the present-day Netherlands in the 14th–16th century. Arguments for (different) choices of replacement stones have been researched and evaluated, in terms of both contemporary perspectives and hindsight. In the period from the second half of the 19th to the late 20th century, various approaches to the choice for replacement stone were found. In this paper, seven periods are distinguished on the basis of specific arguments and criteria that were used for the choice of replacement stone. The paper describes some unexpected combinations of original and restoration material that, most probably, would have never been chosen if only mineralogical composition and origin had been taken into account. Their durability and compatibility are discussed.

Rilem TC 203-RHM: Repair mortars for historic masonry. Repair mortars for historic masonry: From problem to intervention: a decision

This article focuses on repair or replacement mortars for historical buildings. Both the decision process and questions arising are dealt with, in order to better define and illustrate technical requirements for mortars to be used for the repair or restoration of monuments and historic buildings (masonry mortars, plasters, renders…). The article summarizes a longer document, meant to help professionals in their decisions on the interventions, taking into account aspects, which are ranging from the ethics of restoration to the technical requirements.

Definition of Structural Damage Patterns: A Structural Damage Atlas / Definition der Schadensmuster an Tragwerken: Ein Atlas der Tragwerksschäden

The paper proposes a Structural Damage Atlas. The atlas is to be part of the expert system MDDS (Monument Damage Diagnostic System) and is meant as a support for the identification and the explanation of structural damage. It contains a selection of well described and illustrated damage patterns, which may be formed by more than one damage type. They are ordered according to the most probable damaging process(es) causing them. The atlas serves as a reference for making sound hypotheses, which should be further supported by a thorough survey of the building, possibly tests, an analysis of the context in which the damage occurs and by information on the past and present state of the building.

Investigation of commercial ready-mixed mortars for architectural heritage

In conservation practice, operations aiming to restore structural functionality of historical buildings are of primary relevance. Partial rebuilding, the substitution of damaged bricks or blocks and the integration of deteriorated joints are, among others, interventions that require the introduction of new materials in a heterogeneous and aged masonry system. An appropriate durability of these interventions can only be assured if a deep knowledge of the original materials and of their state of conservation is combined with reliable understanding of the behaviour of new materials introduced. The present paper reports the results of the investigation of four commercial ready-mixed mortars based on NHL binders. The mineralogical composition of each product has been evaluated by XRD and polarization-and- fluorescence microscopy (PFM). The molecular composition of the mixes has also been evaluated by FTIR spectroscopy and the morphological features have been studied by SEM observations. The mechanical behaviour has been tested as well. Although supposedly comparable products, the mortars show different compositional features, microstructures, additives and mechanical behaviour. These are essential to evaluate compatibility with historic materials, and should be stated on the technical data sheets, or be determined.

Experimental Study on the Compatibility of a Polysiloxane Treatment with Substrates Loaded with Sodium Sulphate: Influence of the Physical Properties of the Substrates on the Salt Content Limit / Experimentelle Studie zur Verträglichkeit einer Polysiloxan-Behandlung mit einem porösen natriumsulfathaltigen Werkstoff: Einfluss der physikalischen Eigenschaften des Untergrundes auf den kritischen Salzgehalt

Within the framework of an EC program on the compatibility of salt with surface treatments (COST), crystallization tests were carried out on 20 different substrates (limestone, sandstone, brick, tuffeau, tuff and plaster) treated with a polysiloxane (Rhodia H224) or untreated. First, the samples were treated with the hydrophobic agent and the impregnation depth and product consumption were measured. Crystallization tests were carried out for each material using various initial salt contents. Both visual examination of the damage and weighing of loose materials (stone and salt) collected after the test (mass loss) were undertaken to provide qualitative and quantitative test evaluations. The influence of the protective treatment on the observed deterioration depends on the type of substrate. In general, treated samples result in worse spalling or flaking than that observed for untreated specimens. The treatment modifies the way the substrate dries and prevents surface efflorescence formation. But as salts crystallise deeper within the porous network, the treated material suffers other degradation phenomena and eventually, more damage.

Historical Pointing And The Preservation Of ItsValue

Pointing plays both a technical (protective) and an aesthetical role within a wall. Pointing in monuments also possesses a historical, documentary value. Its value and its significance need to be clarified in view of a restoration. The aim of this work is to propose criteria and guidelines to carry out not only technically, but also historically and aesthetically well-considered conservation and restoration activities, thus preserving the value of the pointing within its cultural context. A history of pointing is meant to form the documentary background to evaluate cases of re-pointing. Criteria such as authenticity, homogeneity, durability are discussed in relation to the preservation of the value of pointing. Well-considered restorations should take into account both the technical and the aesthetical compatibility of the (re-)pointing. During a restoration it may be necessary to reach compromises to comply with both criteria, and, therefore, a thorough documentation and motivation of all restoration aspects is essential.

Forever young or ageing naturally

Age and ageing can be felt as negative occurrences. For monuments however, old age is traditionally considered to be a positive quality. Without a certain age the nomination of monument hardly applies. Ageing can be seen as the work of time, which has always been valued: ageing was sometimes even artificially induced in the past. In this paper we will discuss the meaning of ageing in monumental buildings. The fact that in the case of interventions in monuments a perpetual service life is strived for, but restoration ethics clearly put limitations on what can be done, can lead to dilemmas and can make it difficult to take decisions. Cases will be discussed to derive at some criteria to base interventions upon, seeking a balance between mere preventive conservation and rejuvenating practices.

Interpreting Structural Damage in Masonry: Diagnostic Tool and Approach

A sound diagnosis can only be reached starting from a correct interpretation of the damage. This is not always an easy task: symptoms may be misunderstood, alternative hypotheses overlooked, and the context of the damage left unconsidered. This paper aims to offer architects, contractors and engineers a helping hand in interpreting structural damage in masonry. It presents a simple but consistent approach for visual inspections, discussing both essences and pitfalls of the diagnostic process. In addition, it explains the outline of a diagnostic tool that incorporates this approach. The tool, a prototype of which is available for download, offers diagnostic guidance by means of 60 characteristic damage patterns. Since plans are to further develop this tool, the authors would welcome feedback and opporhrnities for cooperation.