Cleaning Techniques in Conservation Practice

Edited by Kyle C. Normandin and Deborah Slaton

Consultant Norman R. Weiss

Managing Editor Jill Pearce


A special issue of the Journal of Architectural Conservation

Volume 11 Number 3 November 2005



Introduction Nicola Ashurst

Masonry Cleaning Technologies: Overview of Current Practice and Techniques Deborah Slaton and Kyle C. Normandin

The White Tower and the Perception of Blackening Carlota M. Grossi and Peter Brimblecombe

Sydney Opera House: Analysis and Cleaning of the Concrete Paul Akhurst, Susan Macdonald, and Trevor Waters

Saint John the Divine: Techniques to Assess Fire Soil Claudia Kavenagh and Christopher John Gembinski

St Paul's Cathedral: Poultice Cleaning of the Interior Martin Stancliffe, Inge De Witte and Eddy De Witte

Laser Cleaning of Sculpture, Monuments and Architectural Detail Martin Cooper

Conservation of Historic Metals by Waterjetting Techniques Joseph Sembrat, Patty Miller, Jee Skavdahl and Lydia Frenzel


Read the Introduction by Nicola Ashurst


Abstracts and Author Information


Masonry Cleaning Technologies

Overview of Current Practice and Techniques

Deborah Slaton and Kyle C. Normandin


The goal of a masonry cleaning programme is typically to remove surface contaminants without damaging the substrate. Cleaning techniques are continually being refined in an effort to provide more effective and environmentally sustainable methods with less potential to damage substrates. Specific goals of new technologies address the preservation of patina while systematically removing various types of soiling deposits, staining, organic growth, and coatings. This paper provides a summary overview of cleaning technologies and techniques currently used in conservation practice as applicable to masonry.

For systems presently used for cleaning masonry, the paper focuses on appropriateness for different substrates and conditions based on laboratory studies, case study examples, and published literature. Systems addressed include water and steam cleaning methods; wet and dry abrasive systems; laser-based cleaning systems; chemical cleaners; coating removal systems; and biocides. The paper examines the conservation precepts and standards that provide a framework for cleaning projects and provides a proposed methodology for masonry cleaning. Issues addressed include the establishment of cleaning criteria, understanding the nature of the substrate and soiling, evaluating advantages and disadvantages of cleaning systems, developing project-specific documents, the importance of in situ trial samples, and providing quality control.


Deborah Slaton

Deborah Slaton is a Senior Consultant with Wiss, Janney, Elstner Associates, Inc. in Northbrook, Illinois, USA. She is a Fellow of the Association for Preservation Technology International and Vice President of the Historic Preservation Education Foundation.

Kyle C. Normandin

Kyle C. Normandin is a Senior Associate with Wiss, Janney, Elstner Associates, Inc. in New York City, New York, USA. He is currently a member of ICOMOS/US and is also a member of American Standards for Testing of Materials Committee E06 on Performance of Buildings.


The White Tower and the Perception of Blackening

Carlota M. Grossi and Peter Brimblecombe


A survey of the White Tower (at the Tower of London) by the authors assessed perceptions of blackening and the relationship between aesthetic damage and darkening of the stonework due to the deposition of soot. Two questionnaires were used to investigate perception, features, causes, and acceptability of blackening at two elevations (north and south-east) of the White Tower with different degrees of blackening. The first impressions of those surveyed were not so much of dirtiness, as of the grandeur or age of the monument. There was also evidence for a patina being seen as an indicator of antiquity or an element of building character among visitors. It is possible for the blackening of historic buildings to achieve a level of acceptability among visitors. Differences in colour appreciation at the two elevations suggested that it was possible to find a relationship between blackness of the stone walls and opinions that the building was dirty. The results of this work were compared with similar surveys of other monuments and overall they hint that visitors hold fairly consistent attitudes towards dark coloration of building surfaces, which can help when making decisions about cleaning.


Dr Carlota M. Grossi
Carlota is a senior research associate at the University of East Anglia (UEA). Her speciality is building stone decay and conservation.

Professor Peter Brimblecombe
Peter is a professor of atmospheric chemistry at UEA with a particular interest in the relationship between air pollution and cultural heritage. 


Sydney Opera House

Analysis and Cleaning of the Concrete

Paul Akhurst, Susan Macdonald and Trevor Waters


This paper discusses the cleaning and conservation of the folded concrete beams, a key architectural feature of Sydney Opera House. This cleaning and conservation work attempts to develop an appropriate method and specific techniques for dealing with the exposed concrete that can be applied to other areas of the building in the future. It describes how the development of the methodology relies on a sound understanding of the historical development and construction of the building and the significance of the concrete in the architectural language of the place. It exemplifies the relationship between the Conservation Plan and the Utzon Design Principles that together provide the framework for decision-making at Sydney Opera House and shows these documents working in practice. Through interviews with labourers, supervisors and engineers, consideration is given to site practices employed in 1964 that have proved to be stable and long-lasting. The development of the approach to the cleaning of the concrete also shows the value of combining oral and published history with laboratory assessment of conservation techniques.


Susan Macdonald BSc(Arch), Barch, MA(Conservation Studies), RIBA
Susan trained as an architect in Australia before spending ten years in London. A former secretary of DOCOMOMO UK and committee member of Australia ICOMOS, she has a particular interest in the conservation of twentieth-century places and has written three books on this subject. Susan is currently the Assistant Director at the NSW Heritage Office in Australia.

Paul Akhurst BSc(Hons), MSc(Cantab)
Paul has degrees in building management and interdisciplinary design for the built environment, and has previously published on change management. He has spent most of the past twenty years working in the UK and Australian construction and facilities management industries. Paul is currently the Director of Facilities at Sydney Opera House.

Trevor Waters BArch
Trevor is one of the few heritage architects in New South Wales employed as a builder rather than a professional consultant. He has worked in this capacity on a number of important projects in New South Wales including St Mary's Cathedral. Trevor developed the method for cleaning the concrete and supervised the site trials and the execution of treatment of the folded concrete slabs at the Sydney Opera House.


Saint John the Divine

Techniques to Assess Fire Soil

Claudia Kavenagh and Christopher John Gembinski


The Cathedral Church of Saint John the Divine is the third largest church structure in the world. It is located on the upper west side of Manhattan in New York City. A fire in December of 2001 badly damaged the stonework of the unfinished north transept and spread thick black smoke through the entire building. After the fire, a comprehensive investigation was undertaken to identify the unique characteristics of the fire soil and then to use that information to determine the extent to which these materials had deposited on surfaces in the building. A direct correlation was made between the materials of construction that burned during the fire and the particles present in samples of soiling removed from throughout the Cathedral. It was therefore possible to establish that the fire soil had penetrated to all areas of the Cathedral and that all surfaces required cleaning. This paper describes the techniques used to carry out the investigation.


Claudia Kavenagh
Claudia Kavenagh received her MS in historic preservation from Columbia University's Graduate School of Architecture, Preservation, and Planning. She is director of the New York offices of Building Conservation Associates Inc (BCA), where her work combines the disciplines of historic preservation and materials conservation for the restoration of buildings and monuments.

Christopher John Gembinski
Christopher Gembinski has been with Building Conservation Associates Inc since 1998. As an experienced conservator, he has performed laboratory analyses using analytical techniques including visual microscopy, x-ray diffraction, ultrasonic testing and Fourier transfer infrared spectroscopy to characterize historic architectural materials. He is a graduate of the University of New Hampshire and received an MS in preservation from the University of Pennsylvania.


St Paul's Cathedral

Poultice Cleaning of the Interior

Martin Stancliffe, Inge De Witte and Eddy De Witte


The construction of St Paul's Cathedral, from the laying of its foundation stone in 1675 to its declared completion in 1710, was the product of the vision and determination of Sir Christopher Wren. But the intervening years have seen the interior paintwork removed, leaving the stonework to become increasingly dirty. A superficial cleaning programme was carried out in the 1930s, but it failed to address the essential problem of the stained and soiled stonework. By the 1990s, concern arose about the dirty condition of the interior. None of the cleaning systems developed in the past twenty years is systematically used for large scale cleaning of interiors of historic buildings. A recent development in interior cleaning is the introduction of peelable poultices based on a specially formulated natural latex dispersion. This paper looks specifically at the conservation methods used for cleaning the interior of St Paul's Cathedral. The paper also focuses on the technical development of the basic poultice, Arte Mundit type I, a custom formulated aqueous dispersion of natural rubber which is designed for application in historic buildings. The results of cleaning studies using this system on the interior of St Paul's are discussed in detail.


Martin Stancliffe MA, FSA, Dip Arch (Cantab), RIBA, AABC
Martin Stancliffe founded Martin Stancliffe Architects in 1975. He was appointed Surveyor to the Fabric of St Paul's Cathedral in 1990. In 2004 his company joined the nationally based architectural practice of Purcell Miller Tritton, and Martin became a Senior Principal with the larger practice.

Inge De Witte
Dr Inge De Witte studied chemistry at the University of Ghent where she finished her PhD in polymer chemistry in 2001. She started her career at FTB Restoration (a company specializing in the production of high quality materials for the preservation and the restoration of wood and stone).

Eddy De Witte
Dr Eddy De Witte is honorary head of department of the Royal Institute for Cultural Heritage in Brussels. He joined the Institute in 1971 where he was head of the Scientific Department from 1987 until his retirement in 2004. His main fields of research related to the long term effectiveness of modern products used in the restoration of historic buildings, and the study of degradation processes of historic building materials.


Laser Cleaning of Sculpture, Monuments and Architectural Detail
Martin Cooper


The use of laser cleaning has now become routine in a number of specialized conservation studios throughout Europe. The technique is most widely applied to sculpture and monuments, for which commercially available laser cleaning systems are now available and are used to provide sensitive, high-quality cleaning. The use of laser cleaning on buildings has tended to be restricted to areas of sculptural and architectural detail, where cleaning of the highest quality is required. The systems employed on such work are usually 'scaled-up' versions of the systems used in conservation studios, i.e. larger more powerful laser systems which allow faster cleaning rates. Transferring laser cleaning from the conservation studios to the relatively harsh environment of the outdoor work site is not as straightforward as it may seem at first. Considerations such as dirt, power supply, handling of equipment, temperature extremes in summer and Summer, and safety must be dealt with if a project is to be completed successfully. Over the past ten years, significant advances have been made in these areas as experience of large-scale outdoor work has been gained and laser cleaning systems have been adapted for such work. This paper describes some of the issues that have been addressed as laser cleaning has moved out of the relative comfort of the conservation studio.


Martin Cooper
Martin is head of the Laser Technology section at Conservation Technologies. He joined the National Museums Liverpool in 1994, shortly after completing a doctorate investigating laser cleaning of sculpture. He has spent over ten years researching and developing the use of laser cleaning in conservation and is now also actively involved in the three-dimensional recording and non-contact replication of artefacts.


Conservation of Historic Metals by Waterjetting Techniques

Joseph Sembrat, Patty Miller, Jee Skavdahl and Lydia Frenzel


Water cleaning has long been used in the conservation of historic metal artefacts and structures and has been fairly well documented in the conservation literature. Typically, low and medium pressure (not exceeding 4,000 psig) water cleaning techniques such as nebulous mist, steam, and power washing have been used to assist the conservator in implementing conservation treatments, not only because they are safe and effective, but also because conservators are not usually fully versed in the principles and technology behind high and ultra-high pressure waterjetting. High to ultra-high pressure (4,000 psig to 50,000 psig) waterjetting is a specialized technique that has been utilized in the commercial cleaning and surface preparation industry for years but has only been used in the conservation field on a handful of projects. In addition to low and medium pressure cleaning techniques, the authors have used high and ultra-high pressure water cleaning techniques extensively on historic metal artefacts for the removal of coatings, corrosion products and soluble salts while making it possible to preserve desirable original coatings and patina materials.

In metal conservation there exists a delicate balance between the goals of the conservation treatment including surface preparation, with its technical aspects of surface profile or roughness, visible cleanliness, and nonvisible cleanliness, and ethical issues of minimal intervention and maximum preservation of original material. Since the late 1980s, conservators have studied the effects of medium and high (not exceeding 35,000 psig) water pressures on bronze monuments in an attempt to replace abrasive blasting techniques to remove unwanted corrosion products while still retaining the aesthetically desirable patina layers. Since then, the authors have performed testing and implemented treatments on steel and aluminium historic artefacts using high and ultra-high waterjetting techniques.

This article will provide a practical introduction to waterjetting technology with specific cases of its use in the conservation of metals. A brief recounting of the application of low to medium pressure waterjetting techniques used by outdoor sculpture conservators will be provided, followed by recent applications of high and ultra-high pressure waterjetting in the conservation of the 'Big Piece', a salvaged steel hull section from the Royal Mail Ship (R.M.S.) Titanic wreck-site and for the conservation of two Saturn V rockets on display at Johnson Space Center in Houston, Texas and the United States Space & Rocket Center in Huntsville, Alabama.


Joseph Sembrat, President and Senior Conservator, Professional Associate, AIC
Joe Sembrat's extensive experience in the treatment of masonry and metals led to the development and creation of Conservation Solutions, Inc (CSI) specializing in the treatment of historic monuments and sculpture, industrial artefacts, and buildings. S

Patty Miller, Conservator, Professional Associate, AIC
As a conservator and project manager for CSI, Patty directs surveys, investigations, testing programs and treatments of historic architecture, monuments and artefacts. Since joining Conservation Solutions Inc. in 2003, she has been pivotal in the expansion of the in-house testing laboratory which enables CSI to service such diverse projects as the restoration of two Saturn V Rockets,and the conservation of hundreds of artefacts salvaged from the R.M.S. Titanic wreck site, including the 17-ton 'Big Piece' of the Titanic hull.

Lydia M. Frenzel, Chief spokesperson for the Advisory Council
Lydia M. Frenzel has a Ph.D. in Chemistry from the University of Texas and is a professional member of the National Speakers Association. She was selected by JPCL as one of the 'Twenty people who have helped change the protective and marine coatings industry in the past 20 years'. 

Jee Skavdahl, Project Manager
Jee Skavdahl is Project Manager for the Saturn V rocket conservation project at the Johnson Space Center in Houston, Texas. She has been closely involved in the management of both the treatment of the Saturn V and in the construction of the temperature and humidity-controlled building which currently houses and protects the Saturn V during the preservation process.

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