Monitoring

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Authors: Steffen Laue, Christine Bläuer, Erwin Stadlbauer

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Introduction and Definition

The term monitoring describes the systematic study and recording of processes with the help of technical instruments or other surveillance systems. Monitoring is used for recording and guidance in developing processes to prevent decay and incidents.

Within conservation and restoration of art and cultural property, monitoring is defined as an observation process to understand the deterioration mechanisms and thus be able to devise appropriate methods to achieve continuous care and long term preservation. Monitoring is the only method to gain knowledge about the complex interaction between all relevant factors within a building, e.g., materials and their properties, temperature and humidity changes, salts, microbiology and anthropogenic influences. Applying the definition to salts in masonry and wall paintings, monitoring entails the systematic recording and observation of salts and/or salt decay as well as environmental parameters like climate or humidity changes [Arnold.etal:1991].

Fundamental and framework conditions

Monitoring of salts and salt decay can, depending on its objectives, be carried out to varying degrees of detail. Prior to beginning the actual monitoring and depending on the object and decay scenario, the aim of the monitoring needs to be defined. Pre-requisite for this is a condition survey of the relevant object together with qualitative and, if necessary, also quantitative analysis of salt content [Blaeuer-Boehm:1994]Christine Bläuer-Böhm (1994).

The aim of monitoring can, for example, serve to answer the following questions:

  • What is the activation mechanism for the crystallization of the salts present?
  • When and in which climatic conditions will the salts cause active damage?
  • What kinetics does the process involve?
  • When is the best time for salt reduction or other intervention measures?
  • What preventive measures are required?

Additionally, it is necessary to consider if monitoring of clearly defined reference surfaces is preferable to monitoring the whole situation. The duration of possible preliminary investigations and subsequent monitoring also needs to be agreed on at the beginning of the project unless its sole purpose is research based.

Prior to undertaking monitoring (which, depending on the nature of the problem, can be carried out before, during or after an intervention) the following points should be determined:

  1. What is to be observed/measured? Examples: Efflorescence, quantitative amount of salt ions, decay (type and form), climate (air temperature, relative humidity, surface temperature), dampness horizons.
  2. Which area is to be observed and measured? To answer this question, in addition to the already mentioned condition survey, it is necessary to consider whether the determination of monitoring locations would require additional preliminary investigations and if so, what are the properties of the object surface and substrate?
  3. How long and at which intervals is monitoring to be carried out? The duration and cycles of observation need to be determined.
  4. What is to be used for monitoring? Which methods and equipment are likely to obtain optimal results? Which methods and equipment are available? Is a macroscopic observation and documentation of the processes sufficient or should recording equipment to measure climatic or surface conditions be used?
  5. How detailed and precise should the recorded data be? How is the monitoring going to be documented? Have relevant guidelines or parameters been defined? At what intervals should the observations/measurements be carried out? How big is the risk that rare but special or important single events are not recorded? What should the quality benchmark be set at? Is the qualitative observation of changes sufficient or is the quantitative recording in the micro and nano scale required, e.g., with laser holography?
  6. Who carries out the monitoring and who evaluates the results? Primarily this concerns the qualifications of the practitioner or commissioning person: Is specialist training/guidance required? Are there objects/situations which require special training? Who interprets the results and who draws up the conclusions in relation to treatment recommendations?

Monitoring is not the final objective in itself but merely a critical step in the process that needs to be followed to finally arrive at a solution to a problem The results will be more meaningful if the relevant questions can be answered and if the procedure to be followed is precisely defined. Monitoring is an adaptable process that requires open minded operators.

Outlook

Monitoring of salts, salt decay and their environmental parameters is a very effective method of gaining understanding about the decay progress on an object. Suitable conservation and restoration measures can be developed based on the monitoring results. It has been shown that optimal monitoring should be prepared with relevant preliminary investigations and organized and executed by trained personnel.

In practice, optimal monitoring is rarely carried out because:

a) It often costs too much time and money (but considerably less than failed intervention measures) and

b) Predominantly because the effectiveness of monitoring is not known to or recognized by many owners or project agents.

Far more education is required in this field for owners and clients as well as researchers, but a willingness to learn and understand is also needed.

Additionally, further fundamental research needs to be carried out to optimize monitoring processes of salts on objects.

Further research subjects to undertake would be among others:

  • Development of monitoring standards: e.g., is it possible to achieve objective observations and how can this be achieved?
  • Monitoring automation - does it make sense and if so, how can it be applied in practice?
  • Which types of professions should be trained in monitoring?
  • Development of so called „low-level-monitoring“ for smaller objects with less funding and/or time available.

Literature overview

Andreas Arnold can, without doubt, be described as a significant pioneer in monitoring salts. Together with his Zurich project team (especially with Andreas Kueng and Konrad Zehnder) he created a substantial basis and provided important impulses for the research and practice in conservation and restoration during the 1980s and ‘90s. A few exemplary articles from the extensive list of publications of this and other project teams are listed here. The following sorting into two groups is intended to facilitate an easy overview and access.

Articles which mainly deal with the basics and investigative methods:

[Arnold.etal:1991]Author: Arnold, Andreas; Zehnder, Konrad
Booktitle: The Conservation of Wall Paintings: Proceedings of a symposium organized by the Coutrauld Institut of Art and the Getty Conservation Institute, London, July 13-16
Editor: Cather, Sharon
Pages: 103-136
Publisher: The Getty Conservation Institute
Title: Monitoring Wall Paintings Affected by soluble Salts
Year: 1991
Link to Google Scholar
, [Bionda:2004]Author: Bionda, Davide
Booktitle: Proceedings of the 10th International Congress on Deterioration and Conservation of Stone, Stockholm, June 27 - July 2
Editor: Kwiatkowski, Daniel and Löfvendahl, Runo
Pages: 627-634
Publisher: ICOMOS Sweden
Title: Methodology for the preventive conservation of sensitive monuments: microclimate and salt activity in a church
Year: 2004
Key: ECOS
Link to Google Scholar
, [Blaeuer-Boehm:1994]Author: Bläuer-Böhm, Christine
Journal: Zeitschrift für Kunsttechnologie und Konservierung
Number: 1
Pages: 86-103
Title: Salzuntersuchungen an Baudenkmälern
Volume: 8
Year: 1994
Link to Google Scholar
, [Franzen:2006]Author: Franzen, Christoph
Booktitle: Praxisoriertierte Forschung in der Denkmalpflege - 10 Jahre IDK. (Beiträge der Fachtagung in Halle 2006)
Editor: IDK
Pages: 31-40
Publisher:
Title: Analytische Begleitung von Salzreduzierungsmaßnahmen
Year: 2006
Link to Google Scholar
, [Guelker.etal:2004]Author: Gülker, Gerd; Hinsch, Klaus; El Jarad, A.
Booktitle: 10th International Congress on Deterioration and Conservation of Stone, Proceedings, Stockholm, June 27 - July 2
Editor: Kwiatkowski, Daniel and Löfvendahl, Runo
Pages: 619-626
Publisher:
Title: Monitoring of salt-induced deformations in porous systems by Microscopic Speckel Pattern Interferometry
Volume: 2
Year: 2004
Link to Google Scholar
, [Hammer:2001]Author: Hammer, Ivo
Journal: Niedersächsische Denkmalpflege
Pages: 401-423
Title: Inhalte der visuellen Dokumentation in der Konservierung/Restaurierung von Wandmalerei/Architekturoberfläche
Volume: 16
Year: 2001
Link to Google Scholar
, [Laue:2002]Address: Mainz
Author: Laue, Steffen
Booktitle: IFS-Tagung 2002: Salze im historischen Natursteinmauerwerk
Editor: Institut für Steinkonservierung e.V. (IFS)
Pages: 19-30
Publisher: IFS, Mainz
Title: Verwitterung von Naturstein durch lösliche Salze an wechselfeuchter Luft
Volume: 14
Year: 2002
Key: IFS Bericht 14
Link to Google Scholar
, [Leitner:2003]Author: Leitner, Heinz
Booktitle: Mauersalze und Architekturoberflächen
Editor: Leitner, Heinz and Laue, Steffen and Siedel, Heiner
Pages: 65-71
Publisher: Hochschule für Bildende Künste
Title: Die Rolle des Restaurators im interdisziplinären Feld der Erhaltung von salzbelasteten Wandmalereien
Year: 2003
Link to Google Scholar
, [Pinchin:2008]Author: Pinchin, S. E.
Journal: Reviews in Conservation
Pages: 33-45
Title: Techniques for monitoring moisture in walls
Volume: 9
Year: 2008
Link to Google Scholar
, [Sawdy:2001]Author: Sawdy, Alison
School: Institute of Archaeology, University College London
Title: The Kinetics of Salt Weathering of Porous Materials: Stone Monuments and Wall Painting
Type: Dissertation
Year: 2001
Key: ECOS
Link to Google Scholar
, [Steiger.etal:1998]Author: Steiger, Michael; Neumann, Hans-Herrmann; Grodten, Torsten; Wittenburg, Christian; Dannecker, Walter
Booktitle: Jahresberichte Steinzerfall - Steinkonservierung 1994-1996
Editor: Snethlage, Rolf
Pages: 61-91
Publisher: IRB-Verlag
Title: Salze in Natursteinmauerwerk - Probennahme, Messung und Interpretation
Year: 1998
Link to Google Scholar
, [WTA_4-5-99/D:1999]Author: WTA-Merkblatt 4-5-99/D
Title: Beurteilung von Mauerwerk, Mauerwerksdiagnostik
Year: 1999
Link to Google Scholar
, [Zier:2002]Author: Zier, Hans-Werner
Booktitle: Salze im historischen Natursteinmauerwerk
Editor: IFS
Pages: 31-39
Publisher: Institut für Steinkonservierung e.V. Mainz
Series: IFS Berichte
Title: Untersuchung der Salzbelastung – Analysenmethoden, Bewertung, Grenzwerte
Volume: 14
Year: 2002
Key: IFS Bericht 14
Link to Google Scholar
.

Articles which primarily provide case studies of investigations of historic structures and wall paintings

[Behrens.etal:2005]Author: Behrens, Elke; Berling, Helmut; Hornschuch, A.; Niemeyer, Rolf; Recker, Bernhard; Schwarz, Hans-Jürgen; Stadlbauer, Erwin
Journal: Berichte zur Denkmalpflege in Niedersachsen
Number: 1
Pages: 9-12
Title: Wandmalerei-Referenzflächen-Monitoring am Beispiel der Stiftskirche Königslutter – Methoden und Erkenntnisse für die praktische Denkmalpflege
Year: 2005
Link to Google Scholar
[Haefner:2003]Author: Häfner, Klaus
Booktitle: Mauersalze und Architekturoberflächen
Editor: Leitner, Heinz and Laue, Steffen and Siedel, Heiner
Pages: 107-120
Publisher: Hochschule für Bildende Künste
Title: Die Verwendung von Kieselsäureester zur Festigung salzbelasteter Wandmalerei
Year: 2003
Link to Google Scholar
[Koehler:2003]Author: Köhler, Wolfram
Booktitle: Mauersalze und Architekturoberflächen
Editor: Leitner, Heinz and Laue, Steffen and Siedel, Heiner
Pages: 51-56
Publisher: Hochschule für Bildende Künste
Title: Zerstörungsfreie Untersuchungsmethoden an salzbelasteten Wandflächen
Year: 2003
Link to Google Scholar
[Laue:2005]Author: Laue, Steffen
Journal: Bauinstandsetzen und Baudenkmalpflege
Number: 6
Pages: 381-390
Title: Salt Weathering of Porous Structures Related to Climate Changes
Volume: 11
Year: 2005
Link to Google Scholar
[Laue:2006]Author: Laue, Steffen
Booktitle: Praxisorientierte Forschung in der Denkmalpflege, 10 Jahre IDK, Beiträge der Fachtagung am 19.9.2006
Editor: Institut ü¼r Diagnostik und Konservierung an Denkmalen in Sachsen und Sachsen-Anhalt e.V.
Pages: 109-115
Publisher:
Title: Untersuchungen zur Schadensdynamik löslicher Salze am Beispiel des Chores im Freiberger Dom
Year: 2006
Link to Google Scholar
[Sanders.etal:2005]Author: Sanders, M. M.; Van Hees, Rob P. J.
Booktitle: Proc. Workshop RILEM Technical Committee 'Repair mortars for historic masonry', January, 2005.
Editor: Groot, C.
Note: St.-Barbara’s Church in Culemborg in the Netherlands has a history of moisture and salt damage to the plaster. In the past several restorations were performed, without a durable result. Finally, in 1997 test panels were applied in order to base the choice for new plastering on in practice proved durability. TNO Building and Construction Research used the church as a case study within the COMPASS project. The salt and moisture load in the walls and in the plaster of test panels in the church were determined. From these investigations, conclusions were drawn concerning the performance of different commercial restoration plasters.
Title: Monitoring of the moisture and salt load in restoration plasters in St. Barbara's church in Culemborg
Year: 2005
Link to Google Scholar
[Sawdy.etal:2005a]Author: Sawdy, Alison; Price, Clifford
Journal: Journal of Cultural Heritage
Note: The use of environmental control as an indirect means of reducing salt damage has long been proposed, but it is only now becoming more feasible with the availability of new information on the thermodynamics of salt behavior. Recent research has led to the development of a computer program, Environmental Control of Salts (ECOS), which utilizes a thermodynamic model to predict which solid minerals will exist in equilibrium at any given temperature and relative humidity, given the ionic composition of the contaminating salts. This, in turn, permits the prediction of the range of ambient relative humidity under which the salt-contaminated object is less at risk of salt damage. This report discusses the application of the ECOS program to provide an insight into the salt deterioration problems affecting the 13th-century wall paintings in the sacristy at Cleeve Abbey, Somerset, UK. The work was realized through a combined process of sampling and analysis, condition assessment and documentation, and environmental monitoring. Analytical data were input to the ECOS program to obtain predictions for the phase transition behavior of the salts present. By drawing together the different investigative strands of the project, the source of significant discrepancies between observed and predicted salt behavior was identified. Once this had been addressed, the resulting thermodynamic calculations not only correlated well with the in situ observations and recordings, but also offered a plausible explanation for the dynamic deterioration processes taking place
Number: 2
Pages: 125-135
Title: Salt damage at Cleeve Abbey, England. Part I: A comparison of theoretical predictions and practical observations
Volume: 6
Year: 2005
Key: ECOS
Link to Google Scholar
[Sawdy.etal:2005b]Author: Sawdy, Alison; Price, Clifford
Journal: Journal of Cultural Heritage
Number: 4
Pages: 361-367
Title: Salt damage at Cleeve Abbey, England. Part II: seasonal variability of salt distribution and implications for sampling strategies
Volume: 6
Year: 2005
Link to Google Scholar
[Tiano.etal:2008]Author: Tiano, P.; Pardini, C.
Booktitle: Proceedings of the International Workshop SMW08, 27.-29. Oktober 2008 in Florenz, edifir, Edizioni Firenze.
Publisher: Edifir, Edizioni Firenze
Title: In situ monitoring of monumental surfaces
Year: 2008
Link to Google Scholar
[Zehnder:2007]Author: Zehnder, Konrad
Journal: Environmental Geology
Number: 2
Pages: 353-367
Title: Long-term monitoring of wall paintings affected by soluble salts
Volume: 52
Year: 2007
Link to Google Scholar

Literature

[Arnold.etal:1991]Arnold, Andreas; Zehnder, Konrad (1991): Monitoring Wall Paintings Affected by soluble Salts. In: Cather, Sharon (eds.): The Conservation of Wall Paintings: Proceedings of a symposium organized by the Coutrauld Institut of Art and the Getty Conservation Institute, London, July 13-16, The Getty Conservation Institute, 103-136, %url%, %doi%Link to Google Scholar
[Behrens.etal:2005]Behrens, Elke; Berling, Helmut; Hornschuch, A.; Niemeyer, Rolf; Recker, Bernhard; Schwarz, Hans-Jürgen; Stadlbauer, Erwin (2005): Wandmalerei-Referenzflächen-Monitoring am Beispiel der Stiftskirche Königslutter – Methoden und Erkenntnisse für die praktische Denkmalpflege. Berichte zur Denkmalpflege in Niedersachsen, %volume% (1), 9-12, %url%, %doi%Link to Google Scholar
[Bionda:2004]Bionda, Davide (2004): Methodology for the preventive conservation of sensitive monuments: microclimate and salt activity in a church. In: Kwiatkowski, Daniel; Löfvendahl, Runo (eds.): Proceedings of the 10th International Congress on Deterioration and Conservation of Stone, Stockholm, June 27 - July 2, ICOMOS Sweden, 627-634, %url%, %doi%Link to Google Scholar
[Blaeuer-Boehm:1994]Bläuer-Böhm, Christine (1994): Salzuntersuchungen an Baudenkmälern. Zeitschrift für Kunsttechnologie und Konservierung, 8 (1), 86-103, %url%, %doi%Link to Google Scholar
[Franzen:2006]Franzen, Christoph (2006): Analytische Begleitung von Salzreduzierungsmaßnahmen. In: IDK (eds.): Praxisoriertierte Forschung in der Denkmalpflege - 10 Jahre IDK. (Beiträge der Fachtagung in Halle 2006), , 31-40, %url%, %doi%Link to Google Scholar
[Guelker.etal:2004]Gülker, Gerd; Hinsch, Klaus; El Jarad, A. (2004): Monitoring of salt-induced deformations in porous systems by Microscopic Speckel Pattern Interferometry. In: Kwiatkowski, Daniel; Löfvendahl, Runo (eds.): 10th International Congress on Deterioration and Conservation of Stone, Proceedings, Stockholm, June 27 - July 2, , 619-626, %url%, %doi%Link to Google Scholar
[Haefner:2003]Häfner, Klaus (2003): Die Verwendung von Kieselsäureester zur Festigung salzbelasteter Wandmalerei. In: Leitner, Heinz; Laue, Steffen; Siedel, Heiner (eds.): Mauersalze und Architekturoberflächen, Hochschule für Bildende Künste, 107-120, %url%, %doi%Link to Google Scholar
[Hammer:2001]Hammer, Ivo (2001): Inhalte der visuellen Dokumentation in der Konservierung/Restaurierung von Wandmalerei/Architekturoberfläche. Niedersächsische Denkmalpflege, 16 (%number%), 401-423, %url%, %doi%Link to Google Scholar
[Koehler:2003]Köhler, Wolfram (2003): Zerstörungsfreie Untersuchungsmethoden an salzbelasteten Wandflächen. In: Leitner, Heinz; Laue, Steffen; Siedel, Heiner (eds.): Mauersalze und Architekturoberflächen, Hochschule für Bildende Künste, 51-56, %url%, %doi%Link to Google Scholar
[Laue:2002]Laue, Steffen (2002): Verwitterung von Naturstein durch lösliche Salze an wechselfeuchter Luft. In: Institut für Steinkonservierung e.V. (IFS) (eds.): IFS-Tagung 2002: Salze im historischen Natursteinmauerwerk, IFS, Mainz, 19-30, %url%, %doi%Link to Google Scholar
[Laue:2005]Laue, Steffen (2005): Salt Weathering of Porous Structures Related to Climate Changes. Bauinstandsetzen und Baudenkmalpflege, 11 (6), 381-390, %url%, %doi%Link to Google Scholar
[Laue:2006]Laue, Steffen (2006): Untersuchungen zur Schadensdynamik löslicher Salze am Beispiel des Chores im Freiberger Dom. In: Institut ü¼r Diagnostik und Konservierung an Denkmalen in Sachsen und Sachsen-Anhalt e.V. (eds.): Praxisorientierte Forschung in der Denkmalpflege, 10 Jahre IDK, Beiträge der Fachtagung am 19.9.2006, , 109-115, %url%, %doi%Link to Google Scholar
[Leitner:2003]Leitner, Heinz (2003): Die Rolle des Restaurators im interdisziplinären Feld der Erhaltung von salzbelasteten Wandmalereien. In: Leitner, Heinz; Laue, Steffen; Siedel, Heiner (eds.): Mauersalze und Architekturoberflächen, Hochschule für Bildende Künste, 65-71, %url%, %doi%Link to Google Scholar
[Pinchin:2008]Pinchin, S. E. (2008): Techniques for monitoring moisture in walls. Reviews in Conservation, 9 (%number%), 33-45, %url%, %doi%Link to Google Scholar
[Sanders.etal:2005]Sanders, M. M.; Van Hees, Rob P. J. (2005): Monitoring of the moisture and salt load in restoration plasters in St. Barbara's church in Culemborg. In: Groot, C. (eds.): Proc. Workshop RILEM Technical Committee 'Repair mortars for historic masonry', January, 2005., %publisher%, %pages%, %url%, %doi%Link to Google Scholar
[Sawdy.etal:2005a]Sawdy, Alison; Price, Clifford (2005): Salt damage at Cleeve Abbey, England. Part I: A comparison of theoretical predictions and practical observations. Journal of Cultural Heritage, 6 (2), 125-135, %url%, 10.1016/j.culher.2005.03.003Link to Google Scholar
[Sawdy.etal:2005b]Sawdy, Alison; Price, Clifford (2005): Salt damage at Cleeve Abbey, England. Part II: seasonal variability of salt distribution and implications for sampling strategies. Journal of Cultural Heritage, 6 (4), 361-367, %url%, %doi%Link to Google Scholar
[Sawdy:2001]Sawdy, Alison (2001): The Kinetics of Salt Weathering of Porous Materials: Stone Monuments and Wall Painting. Dissertation, Institute of Archaeology, University College London, %url%, %doi%Link to Google Scholar
[Steiger.etal:1998]Steiger, Michael; Neumann, Hans-Herrmann; Grodten, Torsten; Wittenburg, Christian; Dannecker, Walter (1998): Salze in Natursteinmauerwerk - Probennahme, Messung und Interpretation. In: Snethlage, Rolf (eds.): Jahresberichte Steinzerfall - Steinkonservierung 1994-1996, IRB-Verlag, 61-91, %url%, %doi%Link to Google Scholar
[Tiano.etal:2008]Tiano, P.; Pardini, C. (2008): In situ monitoring of monumental surfaces. In: %editor%: Proceedings of the International Workshop SMW08, 27.-29. Oktober 2008 in Florenz, edifir, Edizioni Firenze., Edifir, Edizioni Firenze, %pages%, %url%, %doi%Link to Google Scholar
[WTA_4-5-99/D:1999]WTA-Merkblatt 4-5-99/D (1999): Beurteilung von Mauerwerk, Mauerwerksdiagnostik, %howpublished%, %pages% %url%, %doi%Link to Google Scholar
[Zehnder:2007]Zehnder, Konrad (2007): Long-term monitoring of wall paintings affected by soluble salts. Environmental Geology, 52 (2), 353-367, %url%, %doi%Link to Google Scholar
[Zier:2002]Zier, Hans-Werner (2002): Untersuchung der Salzbelastung – Analysenmethoden, Bewertung, Grenzwerte. In: IFS (eds.): Salze im historischen Natursteinmauerwerk, Institut für Steinkonservierung e.V. Mainz, 31-39, %url%, %doi%Link to Google Scholar