Conservation of Cast & Wrought Iron

5 Ethics

The guiding principal in the treatment of historically important buildings is minimal intervention. This means:

Retention of as much existing material as possible.
Repair and consolidation, rather than renewal.
Reversible processes to be used wherever possible.
Use of additional materials to reinforce, strengthen, prop and tie.
Use of traditional materials and techniques.
Recording at all stages of conservation work.
Effective on-going maintenance.

A light-handed approach should be adopted, preserving as much inherited evidence as possible for future generations. Further statements of conservation philosophy are obtainable from English Heritage, the Society for the Protection of Ancient Buildings, and United Kingdom Institute for Conservation.

Conservation Options

If a metal structure is stable, or has achieved equilibrium, it may simply require cleaning and painting to prevent further deterioration. Corrosion or cracking do not necessarily justify intrusive treatment, provided they are not structurally significant, and further deterioration can be prevented by surface treatments such as filling and painting. Historic structures are often required to carry higher loads than those for which they were designed. These should be reduced if possible, or additional components introduced to reduce the stress in original materials. Bonding-on glass or carbon reinforced polymers can dramatically increase strength in some situations with minimal aesthetic penalty, but their long-term performance is unproven.

Dismantling an iron structure allows repairs to be undertaken in controlled workshop conditions, components to be fully painted all round, and new fastenings to be fitted. However, dismantling can be destructive of brittle/rusted components, and there is a risk of losing parts. Dismantling should only be adopted as a last resort, carefully planned, and undertaken by specialists experienced in the conservation of cast and wrought iron work. Parts should be double-tagged with metal labels wired on, and re-erected without delay. Detailed records should be kept at all stages.

New materials should be distinguishable from old, being date-stamped or embossed.

The clip on the left shows castings for a bridge repair.