Caspar Groot

The Effect of Environmental Conditions on Sodium Chloride Damage

Abstract Laboratory weathering tests are important in the field of restoration as they provide a means of estimating, in a relatively short time, the longer-term performance of conservation materials when applied in practice. Accelerated tests to simulate the damage caused to porous materials by soluble salts such as sodium sulphate are well known and highly effective. However, when using sodium chloride the existing test methods are not particularly successful. Research on case studies has shown that the environmental conditions play an important role in determining the occurrence of the decay. Therefore understanding the effect of the environmental conditions on the damage constitutes a first step in the development of an effective weathering test for sodium chloride. The research described in this paper studies the effect of environmental conditions on the decay due to sodium chloride with the ultimate aim of defining an effective laboratory test. The experiments have been performed on two plasters with very different physical, mechanical and mineralogical properties. Different techniques of analysis have been used: mercury intrusion porosimetry, optical polarized microscopy, environmental scanning electron microscopy, chemical analyses and X-ray diffraction. The results obtained highlighted which of the test conditions under evaluation were the most effective. Using this information, a new procedure for an effective accelerated salt weathering test using sodium chloride is proposed.

Historic Mortars: Characterisation, Assessment and Repair. A State-of-the-Art Summary

One hundred and forty-eight original contributions on historic mortars and related subjects were presented at the 2nd Historic mortars conference, which took place in Prague September 22–24, 2010. The papers presented the latest research topics and advancements in this field. The editors vigorously reviewed the papers and selected 34 original contributions to be published in this special post conference publication. These papers constitute the essence of the current State-of-the-Art of research on historic mortars. The summary of these papers is put into a wider context of the past research, current practice and pre-normative activities of RILEM Technical Committees on characterisation of historic mortars (TC 167COM and TC 203RHM).

Two Views on Dealing with Rain Penetration Problems in Historic Fired Clay Brick Masonry

In this paper a comparison is made between two views on solving rain penetration problems in solid historic fired clay brick masonry. The first one aims at protecting the masonry against rain penetration (“rain coat” concept). In the second approach the penetration of rain in the masonry is accepted and the measures taken are focused on improving the capillary moisture transport in the masonry and on the application of materials with favourable drying characteristics and/or the enhancement of the drying conditions (“breathing” concept). It is shown that the often preferred protection approach may result into deterioration of the rain penetration problem instead of diminishing it. Also is shown that the second approach generally leads to a significant drying of the walls, thus providing a sound solution for rain penetration problems in solid historic fired clay brick masonry.

Choosing Mortar Compositions for Repointing of Historic Masonry Under Severe Environmental Conditions

The quality of repointing work in historic masonry is to an important degree determined by the composition of the repair mortar. Apart from this, good workmanship is a basic requirement for durable repointing. Over the past decades awareness has grown that the mortar composition of repointing should always be considered and applied taking into account the hygric and mechanical properties of the existing adjacent materials. Often this is easy enough to realize. However, choosing the composition of a repointing mortar there are situations where various damage risks seem to point at opposing materials properties. In the paper this problem is approximated analysing a number of damage cases with the aim to define more precisely which requirements and to what extent should be maintained. Subsequently, from lab studies and experiences with the application of natural hydraulic lime (NHL) in specific repointing projects a set of requirements is proposed. The context of this repointing study is repair of low-strength historic fired clay brick masonry in the coastal area of the Netherlands; environmental conditions: sea salt laden, heavy rain load and freeze-thaw cycling.

Materials Considerations Regarding Rain Penetration in Historic Fired Clay Brick Masonry

A humidade e uma das principais causas de ocorrencia de anomalias em alvenarias historicas. Deste modo, o controle dos movimentos da humidade em paredes macicas de alvenaria e um instrumento fundamental para a melhoria da durabilidade destas. A investigacao e a experiencia pratica identificaram ja varias das causas que podem influenciar os problemas de permeabilidade em alvenarias. O presente artigo e dedicado aos aspectos materiais relacionados com a penetracao de agua em paredes historicas em alvenaria de barro cozido, construidas com tijolos de absorcao moderada a alta, assentes com argamassas de cal; discutem-se, nomeadamente, a ocorrencia e influencia de parâmetros como a porosidade dos tijolos, infiltracoes nas interfaces e resistencias das juntas de argamassa. Subsequentemente, sao apresentados resultados quantitativos de testes que avaliam os efeitos destes parâmetros na ocorrencia de infiltracoes em paredes macicas de diferentes espessuras. Os resultados das investigacoes permitem apontar algumas recomendacoes as quais recorrer no caso de reparacoes em alvenarias historicas macicas. Finalmente, e ainda dedicada alguma atencao a influencia da mao-de-obra na permeabilidade deste tipo de paredes.

Aspects of salt and moisture transport in restoration plasters and renders = Zum Salz- und Feuchtigkeitstransport in Mörteln und Putzen des Bauinstandsetzens

This paper reports preliminary test results and their analysis on moisture-salt transport in restoration plasters. Using various simple as well as advanced experimental techniques (pursuing a multidisciplinary interpretation on the test results) it was shown that differences in porosity significantly affect moisture-salt transport in plaster-substrate combinations. This observation suggests the need for a more tailored mix design of plasters used in restoration.