黑洞社区

Natural stone paving, whether in granite, limestone, marble or even sandstone, is the perfect adjunct to a stylish building interior or external courtyard. Currently an influx of stones from China and India is opening up the market even further. Not only are natural stones from these developing countries cheaper than those from Europe or even South America, but they come in a wide range of types, colours and textures. And, in the case of China at least, they can be supplied ready-cut to fine tolerances.

The 拢2m makeover of the Victoria & Albert Museum鈥檚 central courtyard in London is a good case in point. In the competition-winning design by landscape architect Kim Wilkie Associates, the courtyard鈥檚 centrepiece is an oval paved in red sandstone and surrounded by water jets, York stone steps and lawns. The red sandstone was imported from northern China, all perfectly cut to fit the complicated double-curved shape of the centrepiece, which is oval in plan, 40 m 脳 20 m in area and dished in section.

The special feature of the stone oval is that it can either be filled with water as a reflecting pool or drained as an arena for displays and receptions. This dual function determined the choice of stone. 鈥淪cottish sandstones were grainy and bright red,鈥� says Gwyn Miles, the V&A鈥檚 project director, 鈥渁nd Indian stones were even more porous. In the end, we went for Chinese stone, partly because it was darker and would reflect the light when filled with water, and partly because it was dense and not porous to the water.鈥� It also cost just a quarter of its European equivalents.

The red sandstone was just one of a large portfolio of stones from northern China supplied by Farrar Natural Stone of Keighley in Yorkshire. 鈥淐hinese stones are totally different from European stones,鈥� says Colin Goble, the firm鈥檚 commercial director. 鈥淭hey鈥檙e much harder, denser and more durable, and white sandstone can even take a polish to look like marble.

鈥淭here鈥檚 no problem about quality, as Chinese stones are absolutely reliable,鈥� he continues. 鈥淲e pretty much get stones delivered for the job that are just like the samples. With European stone, this is a major problem, because the finished product doesn鈥檛 match the samples.鈥�

For the V&A project, the sandstone was also tested for strength, porosity, salt crystallisation and slippiness by stone subcontractor Szerelmey. 鈥淚t passed the performance tests way above other stones,鈥� says Bob Davies, Szerelmey鈥檚 project director.

In Wilkie鈥檚 design, the stone pavings were laid out in 15 concentric oval courses, increasing in size towards the circumference up to 900 脳 900 mm. All the stones were a standard 50 mm thick and separated by 5 mm mortar joints.

For the substrate, a reinforced concrete slab was laid to the same curves and falls as the finished paving and tanked in asphalt. The paving slabs were laid on a 40-50 mm bed of a four parts sand to one part cement mortar and pointed in water resitant ready-mix EasyPoint mortar. A drain hole was cast in the centre of the oval.

Once the sandstone pavings had been precisely designed and dimensioned, Szerelmey supplied the Chinese stonemason with a CD of cutting schedules. The sculptural double-curved shape of the oval meant each stone had to be cut to a different size and shape.

鈥淭he cutting was mechanised, though the angles were cut by hand,鈥� says Farrar鈥檚 Goble. 鈥淭hey were cut to tolerances of just plus or minus 2 mm, which you wouldn鈥檛 get from Europe. The whole assignment was delivered on time in just 10 weeks, and the workmanship was absolutely perfect, with zero rejects. There were about six breakages out of hundreds of slabs, and we cut their replacement from blanks at our works in Keighley.鈥�

The V&A鈥檚 Miles says the paving job delivered by Szerelmey, Farrar and the Chinese quarry is 鈥渁bsolutely great鈥�. Both Goble and Davies are bullish about the promise of their material. 鈥淐hinese stone now takes up 30-40% of our total business,鈥� says Goble. 鈥淚t is only a matter of time before prices start going up,鈥� adds Davies. 鈥淏ut even at double the current price, Chinese stone would still be very good value.鈥�

Project team

client V&A Museum
landscape architect Kim Wilkie Associates
construction manager Bovis Lend Lease
stone subcontractor Szerelmey
structural engineer Dewhurst Macfarlane
sevices engineer Arup
stone supplier Farrar Natural Stone