The Obelisk, which stands in Macquarie Place, Sydney, was constructed between 1817-1818 by Edward Cureton, stonemason, to the design of Francis Greenway, architect, for Governor Lachlan Macquarie. The sandstone comes from a local, but unknown, quarry. It marks the point from which the distances of roads were measured in the early colony.

The deterioration of the Obelisk stonework and responses to that deterioration, have been the subject of much discussion, opinions and unfortunately division, amongst the conservation community in Sydney for the last thirty years: starting in 1978 with an initial study, through to 2009 with the completion of the most comprehensive conservation program the Obelisk ever had.

During this period, the debate waxed and waned without significant conservation (and some more mundane maintenance) being carried out to the monument. The issue that would reignite discussion was the condition and fate of the inscriptions and the loss of other mouldings.

Some reports concluded that conditions that were contributing to deterioration were: proximity of trees contributing to biological growth, surface pollutants from traffic, proximity of the sea giving contamination from salts, existing drainage system not working satisfactorily and contributing to rising damp. Testing to determine the salt types was also carried out during this time.

However, it was not until the curators initiated a rigorous programme of documentary research, site observation, fabric analysis and testing in 2002 that other deterioration mechanisms were identified. These mechanisms are derived from the particular characteristics of this type of stone and its interactions with normal climatic conditions for an outdoor monument: sun and water.

The use of petrographic analysis and careful mapping of the monument greatly assisted understanding about why certain decay mechanisms were occurring and helped to inform conservation responses.

This small casestudy suggests some principles which can assist owners and managers where detailed analysis is required of complex deterioration mechanisms:

1. Do the obvious, simple conservation actions-particularly in relation to water. These will usually provide maximum returns for effort and cost expended.
2. Observe carefully and map the deterioration, but don’t make up your mind about either the cause or the response until hypotheses can be tested and confirmed.
3. Well informed testing informs discussion and reduces conjectural debate. A staged series of tests may be required.

Chronology

The Obelisk and Macquarie Place1

Elisha Long is an architect and did her post graduate study in conservation with the Society for the Protection of Ancient Buildings (SPAB) in the UK. She has worked in private practice in both England and Australia. In 2009 Elisha attended the ICCROM’s 16th International Course on Stone Conservation. Currently she manages technical conservation advice for the Heritage Branch, Dept of Planning (NSW) and continues private practice as Long Blackledge Architects, Sydney.

1. Abbreviated Chronology based on that by: Dr Rosemary Annabel, for Casey and Lowe Pty Ltd, Conservation Issues, The Obelisk, Macquarie Place, Sydney, August 2003. Unpublished report for the City of Sydney.