It involves extreme concentration, hard graft in subzero temperatures and the odd denture in stone, but one academic just can't resist an eight-hour stint of walling, says Olga Wojtas

Taking a summer drive through the British countryside with Mark Kelmanson is an unpredictable business. He is more than likely to stop the car, retrieve his Pennine hammer and start repairing a tumbledown roadside wall. Kelmanson, professor of applied mathematics at Leeds University, does not spend summers lounging on the beach; rather, he indulges his hobby - dry-stone walling. This involves commissions, competitions and shows, but he cannot resist making on-the-spot repairs whenever possible. "It's the reverse of vandalism," he says. And, given that England has 70,000 miles of dry-stone walling, only 4 per cent of which is resistant to damage by animals, he is not short of challenges. "On holiday, I could gladly do eight hours every single day."

Dry-stone walls existed in prehistory, offering shelter to humans, animals and various species of plants and insects. Wallers argue that such constructions are more practical and environmentally friendly than fences because they last longer, can be built on rocky ground, and the stone can be reused.

They were not a feature of the landscape in London, where Kelmanson was born and brought up. He discovered the attraction of the Yorkshire Dales and, by extension, dry-stone walls, only after coming to Leeds to study chemical engineering, a discipline he rapidly abandoned for maths. As a youngster, he was drawn to practical skills such as carpentry, engineering drawing and metalwork. The common factor between these skills, he says, is that they are physically and mentally demanding and cannot be done without concentration. "After I've been walling, I often go back and crack a (mathematical) problem I previously couldn't solve. It gives you such intense concentration that you're divorced from your work, and I've felt much sharper academically afterwards because I cleared my mind," he says.

³ÉÈËVRÊÓƵ

"There are so many white-collar hobbyists within our ranks that this sentiment must be generic across other cerebral professions."

Phil Gilmartin, a professor of biology at Leeds, is another keen waller. A German research student in Kelmanson's department has now caught the bug. "He's my apprentice in walling as well as my postgraduate student in applied maths," Kelmanson says.

³ÉÈËVRÊÓƵ

Kelmanson is a member of the Otley and Yorkshire Dales branch of the Dry Stone Walling Association (DSWA), whose 120 members make it the largest branch in the country. "We've got ex-headmasters, actors, children's story writers, dentists, a heart surgeon and an ex-ballerina," he says. "Wallers are the sort of people who give far more than they take. They're doing very hard work for the satisfaction that they're leaving something that will last for a few hundred years. There are different techniques for different types of stone, but the basic principle is to get strength and durability."

The DSWA is a charity committed to preserving dry-stone walls throughout the UK and to training people in the craft. Kelmanson and other members recently did a three-day display of walling at master-craftsman level at the Great Yorkshire Show. A lorry deposits several tons of limestone and sandstone, and the team then builds, chisels and shapes, following a design they are given. "Many people say what we are doing is not walling. It's almost artistry in stone," he says.

Most of the interest the branch gets at shows is not from farmers but from people who want craftsman-designed stone constructions beside their homes. While Kelmanson stresses that walling offers him an escape from academe, he recognises overlaps with higher education. At exhibitions, audience members often ask wallers how long it took them to learn the skill. "How long did it take Constable to learn to paint? The basics have to be so ingrained that you can deal with any random stone or situation without worrying. The technique should be on automatic pilot so you can concentrate on creativity," he says.

This is what should happen in scientific research - a professor of applied mathematics once told Kelmanson: "It should be the problem that drives the maths, and not vice versa." The creativity displayed by hobby wallers is what distinguishes them from farmers, who simply want a wall as a barrier and will build it as quickly and strongly as possible. "If I go to repair a farm wall, I want to do it as an exercise in self-challenge. I might take chisels and hammers so that I can shape it and carve it and make it look a lot neater. No farmer is likely to do that."

Wallers say that either you have the eye or you haven't. Kelmanson has it. "As you dismantle the old wall, in your mind's eye you can store tens, if not hundreds of stones - for example, one that's fat on the left, thin on the right. You can retain an almost 3-D image before it's reassembled without having to do measurements."

³ÉÈËVRÊÓƵ

His most satisfying project was for a retired colleague living in the north of Scotland, which he designed himself. The repair or exhibition work he carries out is dictated either by what is already there or what task has been set. But on this occasion he worked from his own inspiration, creating a series of follies from some 60 tons of Hopeman sandstone. These included a pyramid containing a wine cooler, a seat shaped like a giant set of dentures and a wall with a flowerbed built into the top of it.

Wallers have strong links with their local communities. The Otley and Yorkshire Dales branch has run courses for children with disabilities and for youths from disadvantaged backgrounds. It has built snail-shaped enclosures for a community playground. Kelmanson has been invited to give a demonstration to young farmers (aged ten to 26) in the area. The branch recently rebuilt the walls round an old graveyard, sustained by bacon sandwiches made by the verger's wife and tea from the Women's Institute urn.

"Having the eye" is arguably more important than mere strength and stamina, and Kelmanson says there are some extremely good female wallers. About 40 per cent of his branch are women.

³ÉÈËVRÊÓƵ

But strength and stamina are nevertheless necessary. Kelmanson has walled for six hours in subzero temperatures. "I had eyes looking like cherries for days afterwards because of the vein rupture," he says. "I typically move between five and six tons in a not particularly hard working day." He has had to put an 89kg stone on top of a wall, and the biggest stone he has single-handedly put into a wall weighed 140kg. "I couldn't move for three days afterwards," he admits.

There are safety techniques for moving stones using levers, small rocks and wedges, but some of the younger and more foolhardy wallers simply use brute force. Most wallers have phenomenally strong arm, leg and stomach muscles, Kelmanson says, but he concedes that many also have back problems. "The theory is that you're meant to bend down and use your knees, but that's not always possible because of uneven ground. Most of us don't look after ourselves properly. The way to do it it not to attack it too ferociously: you get much more rapid progress with a steady pace."

Injuries are generally confined to trapped fingers or thumbs hit with hammers, and hobby wallers beyond retirement age are enviably fit. For Kelmanson, the rewards far outweigh any discomfort. "I walled for 11 hours today in complete isolation on top of a glorious heather-covered Hawksworth Moor, watching hares, lapwings and shepherds gathering sheep amid a chill wind and bright sunshine. Walling is a window on a way of life that, for most of us, disappeared over a generation ago."

There is no sign of Kelmanson giving up his hobby, and his wife accepts that when they are on holiday and he says he's leaving the B&B "for a minute" that he is likely to be gone for hours. "I think she's glad I do it. She says that, whenever I come back from walling, it's with an ear-to-ear grin on my face," he says. "It's hard, it's grimy, but at the end of the day, there's an object that wasn't there before."

³ÉÈËVRÊÓƵ