King of the New Stone Age

If Pierre Bidaud tells you ‘it's good sourcing structural stone from Portugal, as it’s the cheapest in Europe and has very good lead times’, then you would be best heeding the advice.

Since the French stonemason made the UK his home a quarter of a century ago as creative director of his Stonemasonry Company, he remains at the vanguard of a drive to push the use of structural stone – a zeal belied by his otherwise warm and affable demeanour. But make no mistake, along with the likes of Portland supplier Albion Stone, Scottish borders stone supplier Hutton and Norwegian granite company Lundhs – all professional members of The Stone Collective, Bidaud is on a mission to create a ‘New Stone Age’ in this country.

A love of the material is in his bones. Bidaud has been a stone guildsman for 30 years, spending the first decade of that time crossing France to learn his craft before a year working at Gloucester Cathedral in 1994 saw him fall in love with the ‘parametric purity’ of English gothic.

His knowledge of working stone is matched by his appreciation of its architectural context. Viollet-le-Duc and Pugin are casually dropped into a conversation in which he’ll rue Adolf Loos’ championing of stone veneers and express his love for Eric Parry’s structural stone projects and Hopkins Architects’ Portcullis House. The latter, he says, ‘epitomises the new gothic’. In his whistlestop tour of the typology, he co-credits Peter Rice for the post-tensioned stone at Renzo Piano’s stunning Padre Pio church in Italy, and Arup’s Tristram Carfrae for ongoing restoration and innovative stone works at Gaudí’s Sagrada Familia in Barcelona.

A stunning scale model – in stone, naturally – of his firm’s stair for a private house by Foster + Partners in Antalya, Turkey, takes pride of place at the foot of the stone flight in his Clerkenwell office. A stone’s throw away, Bideau collaborated with engineer Webb Yates to realise Groupwork’s 15 Clerkenwell Close. Nominated for the 2021 Stirling Prize, its simple trabeated frame looks about as close to Abbé Laugier’s ‘primitive hut’ concept as we’ve come since the picturesque. And with his ongoing interiors work abroad for high-end clients like LVMH and Hermes, Bidaud is a man at the top of his game.

But this doesn’t stop him being ‘grounded’. Bidaud’s aim is to democratise the use of stone and make it accessible to all as a low-carbon, affordable alternative to concrete. ‘Clerkenwell Close involved just 100m³ of stone; 10m x 10m and 1m deep,’ he says. ‘If you imagine that in concrete, it would’ve been a very different proposition, with steel rebar and aggregate generating far more embodied energy.’ 

It’s a logic expounded in his company brochure, where he illustrates stone’s carbon benefits against other materials, as well as ways of integrating structural stone, both structurally and thermally, into projects of all scales.

He paints a picture of subterranean circularity. ‘The care given to stone extraction is more nuanced than just blasting it away, as with concrete,’ he emphasises. ‘In France, where a lot is quarried underground, spaces created can be used to host data centres, cultivate mushrooms or even store cheese,’ he says. But France’s belief in its craft ‘guilds’, centuries old and nurtured after two world wars, combines with a construction industry that’s far more geared up to using structural stone.

He has worked with Paris-based OnSITE Architecture, Carl Fredrik Svenstedt, Gilles Perraudin and Studiolada, architects who have earned a reputation by realising a host of housing, schools and winery projects nationally. ‘France is as tuned in to the economics of structural stone as concrete and steel ones,’ he tells me, ‘so using it is both viable and affordable.’

While Bidaud is stimulated by working in the UK, where he says engineering design is developed via proving your case rather than the more homogenising, code-based approaches of France, he admits that there remain many challenges to large-scale adoption of structural stone here, the primary one being contractual relationships.

‘The issue in the UK is the power of the main contractor in design-and-build projects,’ he says. ‘Once through tender stages, they have far more power to dictate things and tend to rely on their established supply chains, with stone suppliers already doing good business selling them stone facing slabs to add onto concrete or steel frames.’

But it’s not just UK construction industry inertia, it’s that the government has consistently failed to invest in it. ‘It has been rubbish at developing the kind of stone apprenticeship and training schemes that are commonplace in France, where its guilds have UNESCO status as Intangible Cultural Assets and people are proud to be part of them,’ he says.

‘People are disassociated from means of production and don’t know how things are made,’ he says. This has led to a culture of contractor hegemony. ‘They can say a lot of stuff to scare clients but if we can bring surety to the process, it neutralises those threats,’ he says, adding that prefabrication itself puts pay to any ‘lack of skills’ or the ‘too expensive’ argument.

Prefabrication, it appears, is his magic bullet to overcome entrenched perceptions of structural stone as prohibitively expensive; that and having architects manage their expectations of the homogeneity of a natural material.

Bidaud cites the example of 80 per cent of quarried material being rejected as stone facing due to not being the ‘right’ colour. That, he emphasises, has to stop. ‘Lutyens would have used most of the stone he quarried unless it had fissures in it,’ he says. ‘Architects need to allow the material to speak and not curate the selection. If it’s mechanically sound then it should go in the building.’

And how does one prove that mechanical soundness? Bidaud thinks the way forward may lie in the latest developments in ultrasound tomography, which can be used to check stone for flaws and allow it to be graded, allaying fears for engineers and specifying architects.

It’s also about breaking down stone module sizes to optimise structural integrity and post-tensioning them together using steel rods, as Arup pushed at Sagrada Familia. ‘It means you use the stone’s intrinsic strength while minimising waste,’ he says. But it’s also about shifting the engineering bar that’s dictated by concrete and steel. ‘We need to reconsider if we really need 60mPa concrete performance for a three-to-four storey housing development,’ he says. ‘And if we don’t, what that might mean for promoting stone use.’

Curiously,  Bidaud also envisions the future of structural stone as an invisible one. With climate change driving far more offshore and land-based wind farms and Great British Energy a government priority, he believes we might learn from 18th-century lighthouses and use granite foundations for turbines instead of concrete ones. It’s an argument he feels would better add up if the government doesn’t concede to the concrete industry the carbon capture infrastructure it badly needs in its bid to decarbonise.

In the meantime, Bidaud needs to address concerns on stone’s footprint and the critical aim of specifying locally. And France, he informs me, remains a test bed for that. While the majority of structural stone buildings are in the north east and south west of the country, the stone they use can come from anywhere.

‘They say in France that carpenters are sheep and stonemasons are goats,’ says Bidaud. ‘You can extend that “loner’ thinking to quarries. In a free market, they’ll undercut each other to win work so you’ll find stone shunted from all over the country – even abroad.’

But it seems they are learning from more bullish Portuguese quarries now offering cost stability at scale over time, avoiding the fluctuations that might otherwise hinder stone uptake. But as long as the UK industry default is steel, concrete and perfectly formed stone slivers, all procured at a premium, such benefits won’t be offered.

For Bidaud, such inertia is bound into the industry’s misguided perception of a material that, he firmly believes, can be used economically – in both structural and monetary terms – in buildings of up to 10 storeys. But it’ll take a quantum shift before it does.

‘It thinks cathedrals and pyramids rather than the cottage, barn or warehouse,’ he says. ‘We must address the skills gap and prefabrication to challenge concrete’s market domination. It’s never been about the cost.’