The Association of Preservation Technology Bulletin (Vol LII, No 4, 2021)

The Association of Preservation Technology Bulletin (Vol LII, No 4, 2021) is another thematic one, focusing on wood as a building material. Articles cover wood-conserving projects at a wide range of locations and scales.

Suzana Radivojevic and Chad Randl kick off the edition with a discussion of the importance of plywood in 20th century architecture and housing, and the need for heritage professionals to develop strategies for assessment and conservation. Plywood structural assemblies, finishes and decorative elements are increasingly being considered for their historic significance on national and international heritage lists. It is imperative that heritage professionals develop appropriate evaluation strategies and conservation treatments for historic plywood panels. Specifying appropriate like-for-like contemporary replacement panels, especially for plywood fabricated prior to the 1960s, can be difficult because of changes in production and performance standards.

The authors give a helpful history of plywood and its particular properties, and describe a method of assessing the condition of exterior panels, based on three case studies commissioned between 2017 and 2021. The authors conclude that plywood remains in an early phase of study, documentation and research. The importance of material analysis in architectural conservation is well established, but the analytical methods and protocols for investigating historic plywood are lacking, and clear guidelines for the identification, evaluation and treatment of historic plywood panels are yet to be established.

In a second paper, Ronald W Anthony and Brian D Aschim explain the functions of open-web wood trusses and how they behave under unanticipated loading conditions. These structural framing systems were often used to support the roofs in large buildings that may now start to be considered for statutory protection. The authors explain the factors affecting truss and design factors in loading conditions that can also affect this. They point to the importance of the hardware that connects the trusses together, before setting out five considerations necessary for the assessment of open-web trusses if failures are to be avoided.

Considerations for the use of purified linseed oil on historic wood are considered by Erin Gibbs and Katherine Wonson. Their paper, geared towards professionals unfamiliar with the treatment, sets out the advantages and disadvantages of using this fluid. The authors set out the qualities of linseed oil versus the characteristics of modern coatings and linseed oil paints, and the experience gained since 2012. They conclude that purified linseed oil systems are a promising preservative treatment and a viable option for use on historic wood resources. But they are not a preservation panacea, and when selecting linseed oil paint users must understand what they need and what they are buying. Good specifications are the key to acquiring and applying the optimal product for any given project.

Although wood shingle roofs are uncommon in the UK (referenced in just over 500 listings in England, they are sometimes found on church steeples, for example) they are widely encountered in America but vulnerable and particularly threatened by incidences of wild fires. The paper from Samuel Zabb-Parmley may have some interest to those who may need to consider fire risk, damage and protection (if not wild fires).