Book Review

The Consequences of Past Stonecleaning Intervention on Future Policy and Resources

By Maureen Young, Jonathan Ball, Richard Laing, Pauline Cordiner, and Jeanette Hulls. Edinburgh: Historic Scotland, 2003; 223 pp., illustrations; paper £27.00.

Maintenance and Repair of Cleaned Stone Buildings

By Maureen Young, Jonathan Ball, Richard Laing, and Dennis Urquhart. Edinburgh: Historic Scotland, 2003; 86 pp., illustrations; paper £15.00.

Building Stones of Scotland

By Ewan Hyslop and Andrew McMillan. Edinburgh: Historic Scotland, 2003; 33 pp., illustrations; paper £10.50.

For a nation that is approximately the size of Maine and the population of Minnesota, Scotland's investment in historic preservation research and technical assistance is, quite frankly, phenomenal. The three publications discussed in this review are a sample of what Historic Scotland has in store for those of us curious about and dedicated to contemporary preservation practice.

Historic Scotland is the government agency responsible for protecting and promoting Scotland's built heritage. In the early 1990s, two offices of Historic Scotland—Technical Conservation, Research and Education Group (TCRE) and Heritage Policy Group—launched two remarkable series of publications on heritage conservation. Both series are well prepared and beautifully produced. All titles are available from Historic Scotland (http://www.historic-scotland.gov.uk). Although a few topics in the series are specific to Scotland, our North American colleagues will recognize most topics as useful in their own work.

Three recent publications in the TCRE series address the preservation and conservation of stone buildings: The Consequences of Past Stonecleaning Intervention on Future Policy and Resources, Maintenance and Repair of Cleaned Stone Buildings, and Building Stones of Scotland. The books form a sequenced suite that frames and answers questions about the consequences of previous and future stone cleaning and repair, principles and advice for the "aftercare of cleaned stone buildings," and the availability of stone for preservation work.

The authors of Consequences state three pairs of research objectives: first, to determine the direct effects of stone cleaning on stone decay and to prepare a useful model of performance and life-cycle costs of continued maintenance; second, to scientifically investigate stone decay to determine its nature and causes and to correlate the study results with the effects of stone cleaning; and third, to evaluate practitioners' need for matching stone for repair purposes and make recommendations.

The cleaned/non-cleaned comparisons and their relationship to preservation and life-cycle costs are the heart of the matter. Data for the study were gathered through questionnaires, interviews, building descriptions, and facade assessments. The case study examined pairs of cleaned and never-cleaned granite and sandstone building facades. The authors' research showed that cleaned and repaired sandstone facades have significantly higher incidences of decay than non-cleaned ones. In the long-term, sandstone facades that have been treated required significantly more repair and treatment than facades that have never been treated.

Cost consequences are similar. Since cleaned sandstone facades require repair at higher rates than non-cleaned ones, the long-term extent of stone decay—including repairs due to the eventual results of aggressive cleaning—"would lead to an overall financial loss." Short-term property value increases that may result from cleaning will be offset by the long-term costs of repairing damage.

What created this unfortunate cycle of damage and repair? As TCRE Director Ingval Maxwell describes the situation in his introduction to Consequences, "From the 1960s the cleaning of masonry buildings for aesthetic, commercial and sociological reasons became common place. As a result, and due to a lack of awareness of the potential damaging consequences of the different cleaning processes, much harm was unwittingly inflicted on the stone. Unfortunately, this approach continued for several decades."

Today, perhaps, the industry is changing. In Consequences, a survey of architects experienced with historic structures shows that more than half did not conduct stone cleaning work and about one fourth recognized stone cleaning as potentially damaging to a building. Further, the authors state, "as a consequence of previous research and product developments, [cleaning] methods…have undergone significant changes over this 25 year time period [prior to 1999]. The most aggressive methods of the past (e.g. high pressure grit blasting and highly concentrated chemical cleaning agents) are now seldom employed. Where the cleaning method is significantly different, the post-cleaning behaviour of a recently cleaned façade may therefore differ from that of a similar façcade cleaned 25 years ago."

This is tempered, however, by less promising news. The authors point out that although stone cleaning methods adversely affect stone facades and create long-term damage to stone, the public and building owners generally view stone cleaning favorably because a clean facade reflects well on the building's owner. And more not-so-good news: competent repairs of damaged facades are not cheap, "the long-term effects of stonecleaning on requirements of stone for repair will be significant," and "[p]lanning for material sourcing is currently required to ensure that necessary repair is not hindered by a basic lack of resources, funds or skills."

Recognizing that damage induced by inappropriate cleaning cannot be reversed, the question for preservationists is how to proceed. Historic Scotland sees two possibilities: public education and ongoing research.

Maintenance and Repair follows lockstep the conclusions of Consequences. This advice manual tackles the emerging problems of treated historic buildings. The authors address past, present, and future cleaning by providing pointed and practical advice to practitioners reminiscent of what the National Park Service provides through the Secretary of the Interior's Standards for Historic Preservation and Preservation Briefs. For example, the authors state, "Stone cleaning should always be carried out using the gentlest method…Stone decay is a natural process whose progress may be accelerated or retarded, but never completely halted…Complete soiling removal is not normally possible or desirable and should not be attempted…If short-term gains are outweighed over a time by subsequent losses, then the rationale supporting the initial work is clearly flawed." The publication concludes with a "Check List of Good Practice" that cites important issues necessary to address the consequences of stone cleaning.

For both lay and practitioner readers, Maintenance and Repair interprets the scientific data in Consequences with clear illustrations of the mechanisms and effects of decay. Maintenance and Repair links observed effects to probable causes, potential long-term effects, and appropriate treatment choices (including, importantly, "none"). Maintenance and Repair makes clear the limits of current preservation practices and the need to plan for the future. The authors state that poor quality stone repairs exacerbate damage and urge developing a strategic plan that considers the long-term life of Scotland's stone buildings.

Building Stones of Scotland is a first step toward meeting the challenge of securing an adequate supply of stones for proper repairs. The report summarizes a pilot investigation into existing and missing data on Scottish building stones, and the types of information that would be useful to practitioners. The report makes four principal recommendations for future publications to aid practitioners: a publication that synthesizes existing and new data on Scottish building stones; technical manuals on stone types, properties, use, and performance; a series of regional guides to Scottish building stones to provide more detailed analysis of building stones and quarry sources; and a stones database.

Such a comprehensive and systematic approach to  stone cleaning and repair is characteristic of all of TCRE's and Heritage Policy Group's publications. As demonstrated by the three books discussed here, the methodology and research behind the publications are highly competent, and the interpretation and advice for the practitioner are clear. The publications in TCRE's and Heritage Policy Group's series are recommended for researching particular questions posed by a project, or for commencing or supplementing a preservation practitioner's technical library.

John Robbins
National Park Service