The online resource for the historic environment

3.09 Repair techniques

To assist your understanding of this Unit see BS 7913: 2013:
Section 6: "Significance as part of operational care and other interventions"
Section 7 : "Maintenance"
Section 8: "Heritage and project management"

“In the course of work on an ancient building, points difficult to decide and needing instant decision constantly arise. What needs renewal? How much may be retained? What technical methods should be employed?
Powys, A. R. (1929) Repair of Ancient Buildings

“There is a wide range of repair techniques… which are available to eliminate [or reduce the effect of] the cause [and source] of a defect, stabilise its impact or minimise its rate of spread. These need to be assessed according to their least destructive impact on the original material and on the [asset’s] aesthetic and technical performance. The repair must be compatible with the original construction, its life span, and follow the principles of good conservation practice.”
Stirling, S. (2002)

The use of modern materials and techniques is appropriate to modern assets and should be adopted when undertaking work on them however, historical assets require a totally different set of techniques and methodologies when intervention becomes necessary. It has been demonstrated, beyond doubt, that a sound knowledge of how and why an asset was constructed is an essential tool in any conservation practitioner’s toolbox. The use and incorporation of materials and methods of construction will have been decided upon based on contemporary knowledge at the time of the asset’s creation; coupled with an understanding of use, performance and sourcing of materials relevant at the time of construction – absence of understanding of that fact can lead to inappropriate intervention with potentially damaging if not catastrophic consequences for the asset.

In a 16th century masonry constructed building identify what material should be adopted for pointing repairs and why such material is essential to maintain moisture movement equilibrium within the structure.

By reference to BS 7913: 2013 para 6.7 "Proven techniques" identify where/when use of modern materials or methods might be appropriate.

The choice of method, manner and materials used in any intervention project places a responsibility upon you to ensure that whatever you decide upon has been thoroughly researched and assessed as appropriate. You must cause least damage not only to the fabric of the asset but also to its aesthetic and historic value. You must be self critical of how your interventive methods, use of materials and methods of incorporation might interact with the existing fabric and structure – have you checked on the impact of your proposals?

“The practitioner…must develop a critical and self-critical frame of mind, nurturing the ability to proceed from fact by way of logical argument to defensible – if not inevitable – conclusions.”
Earl, J.

New materials, their use and technology are constantly being advanced. Some new materials or processes may well be appropriate for use on or within an historic asset. Some may be positively damaging to the fabric. You must be aware of these hazards when specifying materials, processes or methods. A full evaluation must precede their introduction.

“New materials and methods of repair will only merit consideration if they have proved themselves by time and if the benefits of their use outweigh any harm that may be caused to the character of the building.”
Pickard, R. D. (1996).

All repairs should be an honest statement of intervention with no attempt to conceal or mislead the observer under close inspection. Repairs may be effected and have minimal visual impact but they should not attempt to deceive the observer into thinking they are original work. Repairs can be reasonably unobtrusive but they must be obvious to close inspect by an informed eye. Where possible they should be reversible, again without loss of character or significance.

How you decide to intervene in respect of any historical asset will be influenced by a whole raft of factors discussed in the preceding sections of this unit. The repair techniques proposed, in order to preserve and conserve a historical asset, will require study and evaluation well before any physical work on site.

You must be able to evaluate the effects of any proposed intervention and ensure that such intervention does not damage the authenticity of the asset. You must be capable of assessing the likely impact of any proposed repair technique to ensure that significance is protected. You must actively consider reversibility of any interventive process to allow for future improvements in technique or technology so that, such improvements may be incorporated without additional loss to the asset’s authenticity and with minimum affect on fabric.

By reference to published material of your choice consider the benefits/disadvantages of undertaking cleaning of a stone monument in a northern industrial town. Consider where cleaning might be appropriate and where it will not be appropriate.

In respect of an 11th century rural church with evidence of internal finishes damage through damp and efflorescent salt deposit, what would be your method of assessing or identifying: the causes and sources of dampness and their long term affect on the building. Assume that the building is constructed in either flint work or stone with elements of timber within the structure. Propose a plan of action to investigate and respond to the problem.

“As conservers of old buildings we are better employed in studying how the buildings… were made and prescribing treatments which make use of long-tested materials and techniques which are most in harmony with what exists.” Earl, J.

To help illustrate the principle of ‘appropriateness’ of intervention consider the following:

During the 19th century the engineer Armstrong constructed one of the earliest examples of a swing bridge, over the River Tyne at Newcastle. One of the pressure vessels controlling the operation of the swing mechanism is irreversibly, and catastrophically damaged, due to internal corrosion. The vessel must be replaced to maintain the swing bridge in operation. What, in your opinion is most important, the maintenance of the ability of the bridge to swing or the perpetuation of the philosophy of minimum intervention and minimum loss of authenticity through minimum interference with original fabric.

See BS 7913: 2013 for guidance.