Professional Builder’s Lee Jones talks to a group of builders for whom preserving old buildings for posterity is an abiding passion
Our sprawling Capital is oft characterised as a collection of villages and, if that is the case, the affluent suburb of Highgate would be amongst the most ‘parish-like’ of its districts. Like London as a whole it is a distinguished by a hugely diverse stock of period properties, many of which are in desperate need of the kind of sensitive restoration of which Conor Meehan and his Triskele Conservation team are expert exponents.
“The materials and techniques we use are chosen to empathise and work with what’s already there,” explains Conor, as he takes a break from the early eighteenth century, end of terrace cottage they are repairing. “Many modern materials, such as the sand and cement that most builders would specify on a project like this one, will be too harsh and unforgiving – they don’t allow a building to breathe and they won’t allow for any movement. By contrast we go back to the old processes, such as making our own hot mixed, lime mortar.”
When this Highgate home was purchased by its present owners it was a victim of severe damp as a result of just such inappropriate materials, where the sand and cement render on the interior of the 9in. solid brickwork was suffocating the walls and stifling their ability to breathe. “The walls in the lounge were totally saturated with damp but by hacking off the cement mix, and leaving it for a month to dry out, we were then able to apply our own remedy”, explains the proprietor of the specialist conservation company.
“By removing it in favour of a three-coat lime plaster, painting with a lime wash and raking back the mortar joints on the exterior in order to repoint with lime mortar, all of the building’s individual components operate in the kind of natural synergy for which they were originally intended. Any moisture in the bricks then makes its way out of the walls through the mortar and, because of the inherent flexibility and softness of lime, the mortar acts as the sacrificial component of the masonry, leaving the soft brick intact when subjected to cycles of freezing and thawing.”
It is an ancient art but one that has its rewards. Like Portland cement in a modern building, Lime is the integral binder of the mix. Limestone is burned in a fire or a kiln, at up to 900°C, driving off the carbon dioxide and leaving the highly volative and alkaline chemical compound known as quick lime. Adding water generates a vigorous reaction and a great deal of heat – hence the term hot mix. In the presence of sand and water these elements will fuse together to produce a very sticky and malleable material that can be used as mortar.
“Lime mortar effectively dries by re-absorbing carbon dioxide (carbonation), and reverting back to a form of calcium carbonate,” explains Triskele Conservation’s experienced artisan bricklayer, Paul Slack, “and the whole process is known as the lime cycle. It does take longer to go off, but it’s a wonderful material to work with. Our ancestors had good reason for putting their faith in lime. London is built on clay, a highly absorbent material, that will expand and contract causing movement in the buildings above in the process. Lime will accommodate this movement whilst cement will inevitably crack.”
Continues Conor: “Almost every pre-World War One building in London has been subject to the inappropriate use of sand and cement at some stage in its life, because it was believed that repointing with it would provide an inherently stronger and water resistant mix, but as a repair on solid brickwork it’s simply inappropriate and harmful”.
Conor Meehan is a Society for the Protection of Ancient Buildings (SPAB) scholar and his approach is typical of that organisation’s mission. Minimum intervention, leaving a visible record of repair, and putting back as much of what is taken out is integral to his philosophy, as is keeping the ancient crafts of the building industry alive. That’s why handmade bricks are sourced wherever replacements are required, and why no attempt has been made to hide the repairs that have been made to the interior of this property’s front door. When Conor’s team removed the plasterboard from the kitchen ceiling they found that the rafters were rotten, but rather than simply discard the old timbers a new roof was built alongside it, leaving old and new as evidence of the work of different generations of craftsmen.
“We call it an honest repair, where the building is a document of its own history – it’s telling a story and we respect each part of that narrative.”
“I’m convinced we’re doing the right thing repairing buildings built with lime with lime,” adds Paul, “Nobody is taught this anymore – most major cities’ housing stock are solid wall construction built originally with lime mortars and plasters and are being repaired using modern, inappropriate materials, such as harsh cements, to devastating effect. They were built to breathe.”