Reinventing the brick - historic restoration and conservation

Materials World magazine
,
7 May 2012

Historic building restoration was among the issues discussed at the Brick Development Association Conservation Day. Eoin Redahan reports.

The Society for the Protection of Ancient Buildings’ (SPAB) manifesto was written all the way back in 1877, but it is just as poignant today. At the Brick Development Association Conservation Day, held in London, UK, on 15 March, delegates troweled scorn on cracked practice.

The wrong choice of building materials will accelerate brick decay. A poorly chosen mortar, for example, will hollow out a building with its deathly bind. According to several delegates, the rigidity and impermeability of cement mortar focuses weathering on a brick’s weaker parts instead of on the mortar itself. The cement remains intact but the clay erodes, leaving a cavernous, boxed effect.

Hydraulic lime offers an alternative. Several speakers lauded the material for its flexibility and breathability. Indeed, lime mortar has been used in buildings for millennia – from Rome’s Pantheon to St Pancras station in London. While cement lets the ice and damp whittle the brick, lime mortar bears more of the erosive brunt.

According to Ian Pritchett, of Lime Technology Ltd in Abingdon, UK, lime mortar has to be re-pointed more frequently than cement – about once every 180 years. However, he claims that a less rigid mortar can benefit recyclability. ‘Hard cement mortars do not allow bricks to be reused. They are recyclable, but they are crushed for use as aggregates.’

The consensus was to accept gentle decay and not to repair unless necessary. SPAB’s Douglas Kent advocated restoring buildings in a manner consistent with the original, which can involve revisiting the ill-advised work of bygone craftspeople. ‘[There was a] Victorian tendency to restore buildings to what they thought they should look like,’ he said. ‘You can lose all of the original work in the process.’

Ideally, reparations should involve using similar materials to the original. At HG Matthews (with the assistance of Dr Gerard Lynch and the Colonial Williamsburg Museum), they mimicked an 18th Century method to produce a range of bricks. Using wood as fuel, they fired bricks in open clamps over a five-night period. Speaking at the event, Jim Matthews, of the Buckinghamshire-based UK company, said this process produced colour variation and glazing effects similar to bricks made in the early 1800s. While these bricks have been sold to a conservation centre and new build, clamp construction was very work-intensive – a huge volume of local wood was used and firing had to be done in continuous 12-hour shifts.

The restorative process can be even more timeconsuming. Emma Simpson and her colleagues at London-based Simpson Brickwork Conservation Ltd repair and reconstruct brick edifices. ‘Dismantling is an extremely laborious process,’ she explains. ‘Every brick and course has to be recorded. The bricks are then taken to the workshop, cleaned and sifted to see how much will survive.’

The restored feature is then dry laid in the workshop to ensure the work is sound. Once the feature is restored to its original position, specialised workers recreate some of the building’s subtle expressions that can only be carved in situ, such as barley twists.

Often, much of the original materials cannot be reused. In a recent chimney reconstruction job, Simpson noted that about 75% of the materials were replaced. After sourcing the correct materials, sketching, creating new bricks and re-building, the aforementioned chimney restoration process took about two months to complete.

One of the finest examples of brickwork restoration rests in the form of St Pancras station in London. Paul Dewick, of Irvine Whitlock, based in Bedford, UK, worked on the recreation of the 19th Century edifice that at one point involved more than 60 bricklayers and stonemasons.

The project exemplifies the difficulty in obtaining suitable materials – 150 samples of mortar, from one kilogramme to a tonne, were inspected. According to Dewick, the globe was scoured for the most appropriate materials, only to settle on materials recommended by the British Geological Survey 10 months previously. But, after eight years, £800m and 60 million bricks, St Pancras stands as an exemplar of historic building restoration.

In a time of brick slips and prefabrication, where robotic arms can lay bricks and apply mortar with expert precision, restoration efforts will get even better. Like many things, though, buildings are better tended by inquiring minds and deft hands.

Number crunching

20:  The number of times stronger today’s Portland cement is than the original prototype

60,000:  The number of UK bricklayers that died in the First World War