Forum Journal & Forum Focus

Keeping the Doors to History Open 

12-09-2015 17:35

For most, the anticipation of pleasant days, an expansive natural landscape, and a premier eighteenth-century Georgian Palladian plantation house is usually reason enough to visit Drayton Hall in the spring. However, this year there were more compelling reasons for a group of preservationists to assemble at John Drayton`s plantation seat along the Ashley River, 12 miles outside of Charleston, South Carolina.

On April 27-29 of this year the National Trust called for a colloquium of architects, engineers, conservators, and other preservationists from Canada, Great Britain, and the United States to address a problem limiting both the longevity of this 18th-century architectural artifact and the ability to carry out the National Trust mission of education and interpretation at Drayton Hall.

This team of advisors, participants, and National Trust staff brought together to decipher the current problem represented the best in the fields of material conservation, architectural preservation, and engineering sciences.

The challenge was to determine, with a minimum of physical and visual intervention, a means of conserving the structural and architectural integrity of the first floor Great Hall plaster ceiling and its successive alterations, while maintaining public access and interpretation of the second-floor Great Drawing Room just above.

The above was not an easy task to be completed in two and a half days, given the circumstances of a modified framing system with a deteriorating mid-19th-century ceiling plaster. To further complicate matters, a matrix of metal bracing, mesh, and additional plaster was installed in 1978 to maintain the decorative ceiling.

In less than a decade this "state-of-the art" solution was failing. Visible cracks, signs of plaster delamination and movement, indicated the eventual loss of historic decorative plasterwork. Preliminary assumptions about the physical condition of this complicated composite system of flooring, joists, new bracing, additional plaster, mesh, lathe, and original plaster could neither render a complete image of the problem nor reveal an immediate solution.

Initial on-site, live-load testing revealed some interesting, but inconclusive, results. Deflection tests indicated that the flooring was three times stiffer than anticipated. Apparent plaster cracks were both old and new, and their discernible pattern led some in the group to determine that insufficient coverage by previous remedial efforts may be one of the reasons for cracking and delamination. Shear stresses were discounted as contributing to the problem while liveload deflection and vibrations remain high on the list of contributing conditions. Additionally, no rate of deterioration had been established.

During the first day`s discussion and testing it became apparent that two distinct issues were entwined requiring separate discussion and resolution. First, how does the National Trust accomplish its mission of education and interpretation while accommodating the necessary analysis and conservation? Second, what is required to determine the most appropriate conservation measures to prevent further deterioration and extend the life of the extant historic fabric?

Moderator Lee Nelson proposed the construction of a bridge as a temporary solution to satisfy the need to reopen the second floor to interpretation. Visitors would walk above the second-floor area without disturbing or stressing the structural system. The bridge would remain in place until the appropriate conservation measures are accomplished, with only temporary visual intervention. High strength, lightweight, man-made fiber structural components (Kelvar and fiberglass) developed for use by the military would allow access to the majority of second-floor rooms without interfering with the testing site. This temporary solution of a 36-inch-wide walkway would permit the inspection and interpretation of the in situ construction and implementation of testing procedures and conservation measures as an enhancement to the educational opportunities offered by the National Trust at Drayton Hall.

With the accessibility problem resolved, the second issue--that of determining the most appropriate conservation measures--became the focus of discussion, debate, and sometimes differing recommendations. The National Trust needed a resolution of acceptable testing procedures that would provide a comprehensive understanding of the conditions from which the steering committee would determine the conservation measures.

Varying opinions from team members over which physical conditions were primary determinants occupied several hours of group dialogue and separate discussions that trailed late into the evening. Materials and construction methods, inherent material and system frequencies (changes measured over time, i.e., temperature and humidity cycles) were of significant concern. Previous remedial attempts had increased the complexity of the problem, leading several of the participants to call for a rational methodology for intensive data collection and expansion of the assessment time.

The result was the formulation of testing procedures governing material characteristics, construction methods, and system interaction. Physical mapping, vibration and deflection tests, and periodic observation procedures were outlined for further investigation. The required information forwarded to the participants would be used to create physical and computer models to be thoroughly tested before new work would actually be performed.

In the intervening months since this gathering took place, the logistics of acquiring, shipping, and installing the temporary bridge has progressed, and installation is estimated to be complete by year`s end. Testing measures are being developed, and the National Trust Office of Technical Services will contract a consultant to map, test, and report its findings to the colloquium participants to determine a conservation protocol.

Collective professional involvement is not new to the National Trust nor to Drayton Hall. Past advisory committees have gathered to offer direction on a number of topics. In fact, Drayton Hall`s conservation and interpretation as an artifact was addressed in 1974 by separate advisory committees on architecture and landscape. However, the 1990 colloquium was the first instance of a committee enjoined to tackle a single conservation problem at a National Trust property. The colloquium illustrates the determination of the National Trust to follow through with its commitment to the mission established for all properties-- i.e., to educate the public about the kinds of places that should be saved, why their preservation is important to the American heritage, and demonstrate how this is accomplished by means of effective preservation techniques.

Publication Date: Fall 1990

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Subtitle:A National Trust Colloquium Investigates Methods of Maintaining Access During the Conservation of Drayton Hall
Author(s):Charles Edwin Chase