HEART OF THE STONE

Lynn Mathias pursues a lifelong passion, repairing walls made of durable flint

Arhythmic tap, tap competes with the chorus of birdsong as Lynn Mathias lightly hits pieces of flint with a metal trowel. Working in the grounds of a Bedfordshire farm, he is rebuilding a Victorian flint boundary wall. Lynn is a flint knapper, a term which stems from the Dutch for breaking or flaking. Flint is a form of quartz occurring in chalk beds both as layers and irregular nodules. It has been used for tools and weapons since the Stone Age, and remains a useful building material today. Flint walls made by the Romans still stand across England, their durability testament to its toughness. In Britain flint is found in a narrow band stretching across south-eastern England from East Anglia to Dorset, and in the South Downs. The wall Lynn is working on is in the village of Kensworth, on the edge of the chalk-enriched Dunstable Downs in the Chiltern Hills. Flint is a popular building material here, much of it found in the beds of a large working quarry at Kensworth Chalk Pit. The geographical location of the flint dictates the areas where Lynn works. “If you go too far east, west or north, you lose it,” he says. “I had a trainee from Sheffield working for me who had never seen flint before.”

Early career

Lynn first worked with flint when he was 16. He helped his father, a bricklayer and stone fixer, to repair a flint section to the lower part of a medieval tithe barn in Edlesborough in Bedfordshire. “My father was the only person I knew whose hobby was his work,” he says. “He had a real passion for it and thankfully I’ve picked that up from him. I just love my job. I like working outside in the warmer months and I also like the creative aspect of the job. It is truly rewarding to restore something to its former glory. I get real satisfaction from that.”

When he was 18, Lynn went to college in St Albans, Hertfordshire, where his studies included historic flint and lime mortar courses. He worked closely with a flint knapper to further hone his craft. Two years later, in 1992, he founded Mathias Restoration with his father. Today Lynn specialises in the repair and restoration of flint and brickwork. Of the two, he prefers to work with flint. “Flint work is more creative. The challenge of working with flint on an old building is trying to get it as good and as close to the original as possible,” he says. “The flint work cannot look like an afterthought.”

A trade little changed

The tools and processes he uses are unaltered since medieval times. Lynn’s hammers, chisels and trowels would all have been familiar to workers centuries ago. The only modern additions are a spirit level, a knee pad to rest the flint on while he splits it, gloves and goggles. The wall he is repairing collapsed during a severe storm. If not rebuilt, the remaining sections may also fall down. The field flint is arranged in a random design, although there is also a horizontal band of brickwork. This is known as a lacing course and is used to level and tie the front and back of the wall together. The repair work will take Lynn up to two months to complete. He is rebuilding the wall to its original height of 6ft 6in (2m), and length of approximately 50ft (15m). It is 131/2in (34cm) wide and solid, filled in with flint and bits of brick. The wall does not have what would be regarded as a modern foundation with poured concrete. Instead, the original flint workers dug down until they found reasonably solid ground and built on that, putting in larger pieces of flint first. Without a solid foundation, the wall naturally bends or bows over time, for example when trees grow nearby, forcing it to move. This natural give prevents it from falling over.

Getting started

The first step is to assess what is there already to ensure it is replicated as much as possible. Lynn studies how the wall was built, what flints were used, their size, colour and texture. He also looks at whether the flints are coursed – laid in a straight row – or not, and what mortar has been used. This information forms a blueprint that he then copies. Once that has been done, he sorts the pieces of field flint left by the damaged wall. “I look for pieces that have good faces – they are the ones that will be on show,” he says. “The misshapen ones I put aside to use in the middle of the wall to consolidate it. Nothing is wasted.” Any soil on the flint is brushed off and unstable pieces are removed. The base area is swept clean with a coarse paint brush. This ensures there is as much contact as possible between the existing flint and the replacement stone. The flint that has been removed for later use is covered with plastic sheeting to keep it dry in case it rains. Flint is not porous, so does not absorb water well. When it rains the water stays on the flint, instead of soaking in or dripping off. Dry stones bond better with moist mortar and are more secure, acting to stabilise the wall. If the flint is wet, it moves, and the wall buckles. Lime mortar is used to hold the flint in place. Lynn uses a soft hydraulic lime mortar due to its inherent flexibility and breathability. “The common mistake is to use cement, which won’t allow any movement and will fracture and crack over time,” he says. The lime mortar mix comprises two parts coarse sand to one part hydraulic lime from Suffolk, and approximately 1 gallon (5 litres) of water. It is mixed the day before he needs it in a conventional drum mixer. This allows time for the mix to ‘fatten’. Lime is extremely porous. It needs as much time as possible to absorb the water and create a better quality mix that is easier to work with. If mixed and used straight away, the mix tends to be

stiff and dry, and can shrink. “Sometimes people add more water the following day if the mix is stiff,” says Lynn. “This makes the mortar too runny and it will not set well. The secret is to simply remix it and the lime mortar will gradually resume its original texture.” Using a spirit level helps ensure the flint in the wall is straight. A string line is fixed to a wooden post at one end and to the existing wall at the other. The string is positioned approximately 4in (10cm) above the flint line that is being laid. This is used as a guide throughout the building process. Two brass plates, called tingles, are placed over the string to stop it sagging and to keep it in place.

Completing the puzzle

The flint for this wall is laid flat in a random design as opposed to a coursed one. For Lynn, the process is similar to a jigsaw puzzle. “It’s instinctive and you get an eye for it,” he says. “You see a gap in the wall and you find the appropriate-sized piece of flint and knit it together. Generally you try to get each piece to touch the one below. If the joint is made too big your eye is instantly drawn to that joint and not the overall look of the wall.” Using a metal trowel, he ladles mortar onto the spot, then fits an appropriately shaped piece of flint onto it. The stone is given a gentle tap with either a metal trowel or hammer. This action squeezes out any excess mortar and creates a tighter fitting joint. Sometimes old Victorian glass bottles, found in fields, are built into a wall to provide decoration. In two days the mortar will have stiffened, but it takes at least eight weeks in dry weather to cure, or dry, completely. As this happens it turns a lighter colour. “The process can be deeply absorbing and I get into a rhythm,” says Lynn. “What is satisfying is when I see a silhouette of a gap and a shape that’s created. Then I find a flint and lay it down and it fits perfectly. I think, ‘Wow! That piece was made for it’.” Dry, cloudy days with no wind provide the perfect weather conditions for working with flint. Too windy or too much sun means the mortar is at risk of drying out and shrinking. If this is allowed to happen, cracks form in it and it will not hold the stones. If this occurs, Lynn gently sprays a fine mist of water over the lime mortar with a fine nozzled water pump spray. He covers the wall with hessian and polythene overnight to ensure the mortar is kept damp and the lime cures. Once he has finished the repair, the wall should stand for another 150 years. “With every job I do, I feel as if I’ve left a legacy for the next generation,” says Lynn. “It is deeply satisfying to see that, by using the same materials and the same design, I have done a sympathetic repair. At the same time I have respected the work done by the original flint knappers.”

When the chalky white cortex of a flint stone is broken, the inner face reveals various colours that range from grey, as pictured here, to orange. › This flint in this wall is in a random design, rather than coursed – that is laid in straight lines – like the brick layer. flint use in britAin Flint is thought to be the remains of sponges that grew on the floor of chalk seas. When the sponge died, the ooze left behind would get trapped in the chalk, slowly hardening into flint. The first extensive use of it for building in this country dates back to the Romans who used it mainly for the cores of composite walls. Coarse, quarried flint was also used in the construction of Saxon and Norman churches, a practice that continued during the Middle Ages. A more architecturally sophisticated use of the material began in earnest at the beginning of the 14th century, when the combination of flint with another material to produce flush work emerged. Flint fell out of favour during the 17th and 18th centuries, but was revived in the late 18th century when flint garden grottos became fashionable. The Victorians produced a whole range of flint buildings, including cottages, church restorations and grand country houses, where the flint was coupled with limestone or brick.

A course of brickwork runs the structure’s length. It provides both decoration and practical purpose, helping to consolidate the front and the back of the wall. Lynn’s hammer would be recognisable to flint knappers from the Middle Ages.

A string erected with the help of a spirit level ensures the wall runs straight and true. Lime mortar is used in flint walls as it is flexible, allowing the wall to move without cracks forming.

Finding the ideal stone to fit a specific gap gives Lynn immense satisfaction. An old glass bottle built into the wall adds further interest. Decorative features are created using pudding stone. This is a naturally formed concrete, containing small stones. The quartz and sediment have bonded together over time to form one big rock. Pudding stone is found in flint-rich fields but is rare.