Fortunately the conservation of natural stone objects in the museum has advanced considerably over the last 30 years and today’s conservators have an armoury of products to choose from.
Outside of the museum the problems are completely different. “Heritage” is perceived as buildings, such as stately homes, castles, churches and cathedrals, and it is in such properties that the restoration of marble and granite can present problems.
The cleaning of both materials is not difficult. There are many products and methods on the market, from simple water washing to complex poultices for removing or diminishing stains. In the U.K. there are many companies who specialize in this type of work and have the experience to deal with delicate stonework, but it is essential to use an expert. Stone Federation Great Britain can give you guidance on that.
Where repairs are required this can cause problems for a number of reasons. Firstly obtaining suitable material can be very difficult, especially marble. The U.K. has very few deposits of marble and what has been quarried has been used in very limited ways, usually confined to buildings in a small area near the quarry.
(At this juncture it is worth making the important point that Purbeck marble is a hard limestone that takes a polish and should be not confused with real marble which is a metamorphic rock).
Because of the lack of indigenous marble the vast majority of marble now in this country has come from overseas, and until more recent times supplies would have come from countries around the Mediterranean. The consequences of this are that it can be difficult, or even impossible, to get matching material for repairs.
Many of the old quarries are shut or “lost” and if found are not an economic proposition to reopen, assuming permission would be granted. Diligent searching around the companies specialising in marble, both here and overseas, may turn up some old long forgotten pieces of marble in a corner of the stone yard.
Granite can present the same problems as marble, except that the range of colours and variations of markings are not so prolific. Furthermore the U.K. has more sources of granite, although not a large colour range, and overseas supplies tended to come from the Scandinavian countries. Some of those materials are still available today. Unfortunately the majority of U.K. granite quarries are now closed and permission to reopen is rarely granted.
Repairs to both materials require a high degree of skill as neither is easy to work. They are both hard, and working on site is never as easy as working inside a workshop. Cutting out damaged areas and letting in new pieces needs to be done with as tight a joint as possible in order to lessen the impact of the repair. This will be easier to do with marble than granite, although, other than impact damage or building movement, granite is less likely to need such repairs as it is not affected by the weather to the same extent as marble.
Marble and the damp U.K. climate are not compatible, the marble going sugary after years in the open. Bodies such as the National Trust cover up statues during the winter months.
“Plastic repair,” or making good, is very difficult due to the nature of both materials and requires a mason with artistic talents. The more veined marbles can present less of a problem due to the variations in colour whereas a plainer marble, such as Carrara, will be more difficult to make good without being noticeable.
When polished, granite is very difficult to make because of its crystalline structure and “depth”. It is almost impossible to replicate and the area made good tends to look dull as it lacks the sparkle that granite possess.
Cleaning of both materials in situ can be done but repolishing granite in situ is very difficult and should not be undertaken without assessing all the pros and cons and possibly trying a test area before final decisions are made.
Floors are one area that needs constant monitoring. The foot traffic in a building originally intended for private use, but now open to the public, will be far in excess of anything imagined when the property was built. This increased use can not only lead to more wear but also dramatically reduce the slip resistance. This is not necessarily a problem when dry, but could be dangerous when wet.
As I have already indicated, when any work is being considered it is vital to talk to a company that is both experienced and knowledgeable.
Stone Federation Great Britain can help with names of suitable companies and for more information you should contact them on 01303 856123 or by email to email@example.com.
The Federation is a valuable source of all sorts of information relating to natural stone. It is the industry’s official trade association, representing employers, liaising with Government on legal affairs, health and safety, technical standards and also developing craftsmanship, training and education.
It produces extremely informative and helpful publications, such as its code of practice for the design and installation of internal natural stone flooring. Again, details are available from the Federation.