Returning to the Stone Age
Stone has been used as a building material for thousands of years and it a testament to its suitability for the task that structures 5,000 years old and more, such as the pyramids in Egypt and the neolithic settlements in Scotland and Ireland, are still standing today.
In some ways, the neolithic structures are even more impressive than the pyramids – because they were built without mortar, which is an answer to anyone who thinks of dry stone walling as a fragile affair.
A huge range of stones have been used for construction, some more suited to it than others. Because stone is heavy and traditionally tended to be used in large blocks, it was advantageous not to have move it too far. Consequently, whatever was found locally was used.
For more important buildings, it has always been considered worth transporting the best, or most significant stones, sometimes quite considerable distances, especially after the canals, railways and roads had been built and transport and handling was mechanised by steam, petrol and hydraulics.
Quite how huge stones were moved and piled on top of each other in earlier times remains a matter of conjecture. How were the Welsh stones moved to Salisbury Plain for Stonehenge? How were the blocks raised, layer upon layer, for the pyramids? People have proposed answers, but we do not know for sure.
The diversity of stone used for building has helped create the characters of the areas where stone was found and used, such as the Cotswolds, where the warm yellowish limestone has played a considerable role in creating a distinctive and attractive built environment. In Cornwall, the granite has led to a much harsher and more rugged appearance.
The nature of the local stones also contributed to the vernacular design, which had to take into account the materials to hand for building.
These days, with a high level of mechanised transport and handling, it is easier to extract, process, deliver and install stone for construction and now stone from all over the world is carried thousands of miles to where it will be used.
Suppliers seek out the most attractive materials and can transport them from wherever they are found to wherever people want to use them for any of the diverse roles to which stone is put – outside and inside walls of buildings, floors, worktops, furniture, roofing and cladding slates, paving and walling for hard landscaping, even as the most traditional of all uses of stone – memorials.
Stone cannot really be considered as one material – it is a diversity of materials created in a variety of ways from various minerals.
There are three broad categories of stone – igneous, sedimentary and metamorphic.
Igneous stones are those created by the Earth itself. They are magma spewed out from volcanoes or squeezed up through cracks in the crust. These are what the stone industry tends to lump together as granites, much to the dismay of geologists, who are always happy to point out the error of the stone industry in describing materials under catch-all headings such as granite or marble. Geologists enjoy debunking the myth that there are black granites, so popular as kitchen worktops. These materials are not true granites in a geological sense, but are usually schist, basalts or some other dense, polishable rock.
Marble is even more troublesome. Marble is one of the metamorphic rocks. It started off as limestone and has been transformed by being buried in the Earth’s crust under extremes of heat and pressure into a recrystallised material.
But the process is not always complete and the limestone can be ‘contaminated’ with other minerals, giving rise to a range of minerals that geologists identify separately. The stone industry lumps the most decorative of them together under the simplifying heading of ‘marble’. It does not, however, consider all metamorphic rocks marble, because slate, which is quite separate, is also metamorphic.
The sedimentary rocks are usually limestones and sandstones with some mudstones. These form the largest part of the building stones extracted and used in the UK. Portland, for example, from which much of London has been constructed since Sir Christopher Wren started rebuilding it after the Great Fire of 1666, is a limestone.
Look down at the ground in London and you will often find you are walking on Yorkstone, which is a sandstone. It is often protected by harder granite kerbs that were traditionally from Cornwall. On the roofs you might well find dark grey slates from Wales or green slates from Cumbria. These days, stones used are just as likely to be sourced from all over the world.
Stone, in all its diversity, is unarguably a wonderful building material, bestowing an unequalled sense of quality on the projects for which it is used.
And it is one of the most sustainable building materials. It is extracted and processed using low energy machines and equipment. It depends on the material and its use, but producing stone products typically uses a tiny fraction of the energy required to fire the kilns for burning the limestone that makes cement used in concrete. And it has environmental advantages in use, if architects sensibly employ its thermal mass to reduce the amount of energy needed to heat and cool buildings.
It is no wonder that, with all its practical and aesthetic advantages, construction is returning to the stone age.