Piccadilly’s classical cover up

Most new office developments in central London, the ones in the media spotlight at least, are steel and glass constructions.

But 198-202 Piccadilly is different. Its facades are rich in classical detailing: granite columns, French stone pilasters and giant urns vie for attention. Its structure and the way it was erected, however, is thoroughly modern. The result may look hand built, but in reality it’s a steel frame clad with stone panels sealed with seemingly invisible mastic joints.

It was just such ‘dishonesty’ – a desire to hide rather than reveal structure – that led to the modernist movement a hundred years ago and resulted in buildings like 198-202 Piccadilly’s neighbour, grade II-listed and occupied by bookseller Waterstone’s, finding favour within our towns and cities. Their simple, unadorned facades are a direct response to the mouldings and insets used in classical architecture which, while certainly pretty, double up as cover for construction junctions.

Similar tricks, along with some new ones, such as stone dusting the mastic for example, were used on this contemporary-but-classical build by the design team of Robert Adam Architects and cladding specialist Marble Mosaic Company. Tolerances were also a big issue – they had to be as small as was mechanically possible. With main contractor Sir Robert McAlpine, they clearly got the formula right: it not only looks authentic, it was completed on time and to budget.

Robert Adam Architects was appointed by client Standard Life to design a mixed use scheme – three floors of office space with a double height ground floor for high end retailers – on the busy Piccadilly site after previous designs had been rejected by planning (see box overleaf). Robert Adam’s solution was to ‘wrap’ a steel frame with a classical stone facade. The architect, which has a reputation for delivering high-quality classical architecture, chose The Marble Mosaic Company for the stone package design and installation works and involved the West Country firm as early as it could on the two-stage JCT contract.

Paul Hanvey (ACIOB), technical director at Robert Adam and the project’s contract administrator, says: ‘We had to assess our options – hand set or panelised. Hand setting would require scaffolding and lifts and labour would be an issue. Sir Robert McAlpine had concerns regarding holding on to stonemasons and keeping the work on programme and so was keen on panelised from the start. We were only happy with a panelised approach, however, if we could develop the design, cut the tolerances and spray the mastic. These were conditional.’

In conjunction with the structural engineer the architect set a very tight tolerance specification: the joints were to be 6mm plus or minus 2. It was also agreed with Marble Mosaic that the stonework itself would have a tolerance of 2mm to negate the potential of cumulative tolerances creating extra-wide and unsightly joints once the panels were put in place. Furthermore, extra stiffening was designed into the steel frame to minimise sway and movement. Panel sizes were fixed by the crane’s capacity of 6 tonnes.

In practice two joint sizes have been deployed. Hanvey explains: ‘Classical buildings have lots of recesses and changes of plane in their facades. It’s an ideal surface to incorporate joints and hide them. So we agreed to a 13mm plus or minus two in recessed locations but adhered to the fine tolerances where they were clearly exposed.’

Paul Hanvey, Robert Adam Architects

Robert Mcalpine had concerns regarding holding on to stonemasons and keeping the work on programme.

While a 6mm joint is pretty fine, it still requires a mastic seal and its shiny white finish is a pet hate of the architect. So the design team set about creating a mix that could be applied to the mastic to blend it with the stone. Initially, the other team members were doubtful it could be done, says Hanvey. ‘They were sceptical at first but the last thing you want to see is a horrible shiny mastic joint on a stone building.’

Once convinced, Marble Mosaic threw itself into the task and together with the architect and mastic specialist Adshead Radcliffe it created a ‘spray dust’ that could be applied to the mastic while it was still sticky. The dusting is done by abseiling workmen wielding spray nozzles and compressors. A fine stone grit is blown into the mastic during the first 20 minutes of application, creating a rough surface that matches the stone in colour and texture.

The colour match is good, but it could be subject to colouration in the long term. Principle architect Robert Adam says he has ‘some hope that long term the contrast won’t be too great’.

Dennis Vittle (ACIOB), joint MD of Marble Mosaic says it has installed three panels per day on average. ‘Accuracy of placement was essential and there were some complicated sections of stone, particularly at the two corners, one of which is radial, the other being octagonal.’

The strategy worked and Vittle says his firm completed the package over a week early and within budget.

As well as the savings made by opting for cladding panels over hand setting, choice of materials further reduced costs by £0.4m. The majority of the stone is Portland stone, a cheaper alternative to a French limestone that was also in the running. But the biggest savings came from opting for granite from – surprise, surprise – China. According to Hanvey, who visited China with the main contractor and stone specialist, production facilities were basic, but the carvings were accurate (and done by an army of female stonemasons) and deliveries were shipped on time. He adds: ‘For the more complex carvings we created 1:1 mock ups and sent them to China for reference.’

The £21m contract is now complete and fitout is under way. Visiting the building with Vittle and taking a walk around its perimeter one can’t help but be impressed with the quality of the appearance, the blond sandstone gleaming in the spring sunshine and the mastic, to all intents and purposes, invisible. The richly expressive classical facades are further enlivened by granite and bronze details, with sculpted heads of ancient gods, and ornate column capitals adding to the visual treat. ‘It makes the Waterstone’s building look rather ordinary, don’t you think?’ says Vittle.

The result, according to Hanvey is ‘very satisfying’. He says: ‘100 years ago when you produced these type of buildings the Regs didn’t exist. So to achieve that style and appearance and incorporating the current Regs, it’s quite a challenge. But we’ve shown it can be done.’