Editorial

Costs for maintenance and restoration of built monuments in Europe are high, sometimes due to the choice of inadequate repair materials or inadequate application. For masonry mortars and pointing mortars research has already been performed on a European level. In the field of mortars for renders and plasters this was not the case, while still many questions have to be solved. Salt decay processes are amongst the most recurrent causes of damage to masonry and masonry finishes like renders and plasters and, as has to be stressed, the mechanisms are still poorly understood. Special rendering systems are available on the market, which are meant to achieve a longer service life in the presence of salts and moisture, but also more traditional solutions are in use. Experience in the field has shown that, even in the case of special mortars, failures regularly occur. This makes the situation for end-users, with respect to the choice of the most appropriate rendering mortar, little transparent.

For these reasons the European COMPASS project (Compatibility of Plasters and Renders with Salt loaded Substrates in Historic Buildings) was launched and executed (2002-2005). In order to improve the current situation the COMPASS project was focused on the development of the following three fields of knowledge: (I) a model describing the decay process and experiments and field evaluation to validate the model (II) requirements for rendering mortars as a function of different application conditions and (III) end-user guidelines (in the form of an expert system) for the choice of the most adequate solution in a given situation.

In this special issue the attention is focused on the research results of in-depth programs within the COMPASS project. The main objective of the in-depth research was to develop a transport and degradation model for the substrate-render combination: i.e. to give a sound description of the degradation mechanisms. To this end theoretical and experimental methods have been applied to study the moisture/salt transport and degradation mechanisms. For the development of the theoretical models unsaturated flow theories were used. In the experimental studies the following methods were applied:

NMR, to measure moisture and salt (ion) movements with a very high spatial resolution

ESEM, to measure the position and type of salts in a specimen

Mercury porosimetry, to determine the pore size distribution in test specimens

Climatic cabinet, to determine the influence of environmental conditions on moisture/salt transport and crystallisation/hydration

In the research results presented in this special issue an attempt is made to correlate the theoretical findings with field study results on salt distribution and damage mechanisms, experimental studies on dilation during crystallisation-dissolution cycling and results of the development of an accelerated salt damage test.

Guest editors: Caspar Groot and Rob van Hees

Acknowledgement

Caspar Groot – one of the editors of this issue – was secretary of HERON until January 2006. A position that he hold for almost 10 years. Apart from his crucial input to the editorial board meetings he did the communications with the authors and the reviewers, he was responsible for the final assembly of the journal and took care of the cooperation with publishers and printing companies. He coached HERON through many changes in editorial board and commercial partners. Caspar has an international reputation in the fields of modelling of masonry and the restoration of buildings. He also contributed a number of papers on these topics to HERON. The editorial board likes to thank Caspar for his indispensable contribution to the quality of HERON over all these years.

Editor-in-chief: Bert Sluys