Natural stone and retrofit – a natural fit

The Stone Federation on the restoration and retrofit of public buildings and natural stone as a building material

As specifiers become increasingly aware that a ‘business as usual’ approach to the carbon impacts of architecture and construction is no longer an option, there is a fresh drive to consider the alternatives.
    
In September of 2019, Architects’ Journal launched the RetroFirst campaign aimed at prioritising the retrofitting of existing buildings over demolition and rebuild.
    
The campaign sits alongside several other initiatives all seeking to encourage architects to try and work with the existing structure as a more sustainable approach to architecture and construction.
    
Retrofitting, or adding something new to something existing is not a new approach in construction. Through good maintenance and conservation schemes, hundreds, if not thousands of natural stone structures have stood for centuries. Many of Great Britain’s major cities have been architecturally defined by natural stone buildings that have stood the test of time, while buildings made from other materials have aged poorly and required demolition.
    
Natural stone is one of the most durable of all construction materials giving maintenance teams the option to redress, clean and replace damaged elements without the need to flatten the building and start again.
    
The Repair & Restoration category at the Natural Stone Awards is full of fantastic examples of buildings that have been retrofitted, structures that, had they been constructed in concrete or other less durable materials, would have been demolished.
    
One of the key factors is the decision by the original architects to choose natural stone. Unfortunately, the last few decades have seen the construction sector steer further and further away from durable building solutions and erred more on the side of quick, cheap but relatively temporary material choices. It is encouraging to see a shift away from this specification model as the architectural industry is challenging itself to change its habits and techniques to deliver a more sustainable solution.
    
The Architects’ Journal campaign references a study by the Department for the Environment, Food and Rural Affairs (DEFRA) that found that of the 200 million tonnes of waste generated in Britain annually, 63 per cent is construction debris.
    
It is for this reason, among others that, proper maintenance is essential and if this is carried out periodically with suitable skill and understanding, the greater will be the environmental and practical advantages in the preservation of the structure.
    
It is essential that cleaning should be carried out by fully trained operatives in order to avoid any damage being caused by an inappropriate cleaning method or an incompetent operative. It should be remembered that decay can often take place around an open joint or cracked stone which cannot be seen if they are obscured by dirt or heavy soiling.
    
The Stone Heritage Group is an arm of Stone Federation dedicated to resourcing the heritage sector of the natural stone industry and promoting the use of Federation members for projects of this nature. Almost 50 per cent of the overall membership work within the conservation and restoration sector, and it plays a large part in the overall natural stone arena.
    
Much of the work of Stone Federation’s heritage members involves the cleaning of natural stone buildings and is a topic where correct procedure is vital.
    
The cleaning of a building is no simple matter and there are special considerations which call for a high degree of expertise in all elements and stages of stone cleaning. Specialised knowledge is necessary for the correct specification to be given for each building.
    
In the past, it was smoke emissions from the burning of coal that caused the soiling of buildings but today it is vehicle exhaust emissions and acid rain that are mainly responsible. Many studies have shown that there are advantages to cleaning buildings on a regular basis.
    
The correct cleaning of natural stone is a priority for the sector as much of the architectural heritage of the country is made from this material. Stone is one of the most durable of all building materials and compares very favourably with others from an economic as well as an aesthetic point of view, especially when maintenance and whole life costs are taken into account.
    
Nevertheless, proper maintenance is essential and if this is carried out periodically with suitable skill and understanding, the greater will be the environmental and practical advantages in the preservation of the structure. What must be stressed however, is that in the wrong hands and by the use of the wrong process for the material in question, much harm can be caused with unsightly effects, some of which may not become apparent for some months after the cleaning has been completed and will be difficult, if not impossible, to remedy. This is why it is imperative to involve a member of Stone Federation at an early stage when the cleaning is being considered.
    
It is essential that cleaning should be carried out by fully trained operatives in order to avoid any damage being caused by an inappropriate cleaning method or an incompetent operative. It should be remembered that decay can often take place around an open joint or cracked stone which cannot be seen if they are obscured by dirt or heavy soiling.
    
Reference should also be made to BS 8221 (part 1): 2012 Code of Practice for Cleaning and Surface Repair of Buildings. Stone Federation also produces other relevant publications and these can be found on their website at www.stonefed.org.uk.
    
The Stone Federation Great Britain Guide to Best Practice is based on the relevant parts of a number of British Standards relating to masonry cleaning and incorporates current good practice. It sets out the principal factors involved when deciding to clean and maintain buildings incorporating different types of masonry.
    
This document’s aim is to give subjective advice as a guide; however, it is by no means a definitive guide. Variables exist with every project and no two projects are the same.
    
To order your copy of this publication you can email matt@stonefed.org.uk. Please note that our publications are not available to companies that could be members but are not.