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Spolia - the two-thousand-year-old circular economy

Set in a disused raspberry farm west of London, Paye Stonework and Restoration’s storage facility boasts an incredible archive of stone. The stone is arranged library style with a system noting the building the stone came from, the course - the horizontal layer of stone - and its position on the building’s façade. There are entire deconstructed stone facades here, waiting to be restored and returned to site. The ceiling had to be raised by 6ft to accommodate all of the stone and when I visited, the space was being expanded to make room to store the next dismantled building.


I spoke to PAYE Restoration and Stonework Director Robert Greer who showed me around the vast storage space and explained the benefits and challenges of reusing stone, a practice named Spolia. For pronunciation think ‘Yo’ or ‘bro’!  

Spolia has been around for a long time, where did it all start?

2000 years ago, with the Roman’s where spolia was put into practice depending on who had the upper hand in the empire at the time. The Arch of Constantine is made-up of stone removed from earlier monuments to Hadrian, Trajan and Marcus Aurelius. Constantine took down the last three emperors’ monuments, built a monument to himself, and replaced their heads with his own.


There is an incredible amount of stone here.

It’s such a great opportunity to have this space. We can set up a facility purely for cutting stone that may be here for five or six years. Depending where the project is and the size of the stones we’re cutting, we may have to move it. It all needs to be together. We’re trying to avoid undermining our whole ethos by moving stone around the country.

Do you use an agreed upon spolia reference categorisation or is it particular to Paye?

We leave it with the masons to come up with their own ideas in consultation with the draughtsmen. When you’ve got over six thousand stones you need everybody to buy into the process to avoid errors. The whole process of recording, cataloguing, dimensioning and dismantling is based on confidence, with correct measurements and numbering. We can now get the Revit model to talk to the excel spreadsheet where we’ve populated all the information about each stone. We’ve got an algorithm that will check for discrepancies early on and then right the way through the dismantling process so that we always have the ability to correct as we go along.


So you’re able to produce an accurate resource of all of this material?

It’s accurate and also dynamic, things do change. We look at a stone and realise that what we thought was an internal corner is actually a joint that was so hidden by carbonation and dirt that we couldn’t read it.


An archaeology of stone; you’re discovering as your dismantling?

That’s always happening. We discover issues such as Regents Street disease where the steel frame corrodes and fractures the stones leaving a lot of stone which is no longer suitable. Normally the grand cornices fail. Typical early 20thcentury issues!

What happens to the stone if it doesn't get to be in your safe hands? What's the worst outcome?

The outcome is that you end up saying it's not possible to dismantle and rebuild, you say it's too complex there's too many unknowns and problems. Or you end up delivering stone to site that’s the wrong size and they either have to be cut on site or taken off site, cut and brought back, then you start to increase the labour cost on the project. Our technical investment should stop those errors from creeping in later.

Where does the conversation on spolia start in a project and who has it?

It happens at stage two. The client will appoint an architect and they’ll start to work out what to do with the building with some kind of flexible intent. We’ll get called and asked about probability and the risk associated with undertaking works. We’ll put a budget together to dismantle and rebuild and see if that works with their ideas.


Is it an enlightened developer or will it be the architect pushing the conversation?

There are certain architects aware of the process. MAKE Architects, AHMM and Eric Parry are architects who understand what’s going on. It’s predominantly a London phenomenon at the moment and maybe that's because the London lease market is providing the ability to be ambitious. The most common scenario is bespoke projects where we are dismantling and rebuilding.


How is the stone dismantled?

We drill a hole in the top, in the centroid of the stone. We still use a lifting eye called a Lewis pin which works like scissors in opposite way that they would, so as you apply load they open out and pinch the sides of the hole to lift the stone. Two tons of stone can be lifted using a Lewis pin, enough to get straps underneath.


We vibrate the joint at the front of the stone so that as it moves it doesn’t flush the edge of the stone. We then use another quarrying technique called ‘plug and feathers’.  When they split blocks in the quarry, they drill a hole and put two feathers in and then the plug in the middle. They do that every six inches along the perp joint and tap them in one by one. It slowly puts lateral force into the joint right and at some point it just breaks, therefore you have de-bonded that stone from the stones around it.


The stone breaks cleanly then?

Yes, unless it's built between 1908 about 1920 when they used a rich cementitious grout. What we find sometimes is that the stone fails before the grout. We have to be a bit more brutal in the way that we have to cut deeper. That’s a last resort.

Will each building present a different kind of scenario, or are there similarities in what you find?  

They are all different. In 1909 they realised they could use structural steel as a material to support the floors and between 1909 and 1939 engineering conservatism started to evaporate. During that time engineers would have their own way of installing a masonry façade.


So, you’re seeing the personality of the engineer.  

We have one building we’re repairing at the moment, and it's built in three phases by two architects and three engineers over 20-year period. The outside looks exactly the same but the way of achieving it was totally different. What we have in our favour is that we use ground penetrating radar (GPR) so that we can work out how thick the stone is and know we're going to have as an element to work with what we need to do to try and reuse that. This is beneficial where stone can be cut back to a line with everything behind becoming spolia. The stone will go back on the building with the rest going into our block store to be cut and used again. The client is keen to make this work as atrium cladding.


Then the client is aware of what is unpicked and the potential of it - so they get an atrium and the façade put back.

They get atrium cladding and can confidently say they are using repurposed material and therefore the carbon cost is really just the production element not the material.


How is technology shaping the work you do?

Every year we're trying to do something new. We're looking at using NFC tags so the way that you chip your dog with a little tag. Discs printed up with numbers will be attached to the stone which you can scan with your phone and get all of the information on that stone. You can then check for any discrepancies as it flags to the draughtsman to check the model. We are using ai to achieve the accuracy we need.

With the conversation around reuse gaining momentum, are you seeing a shift in the awareness of spolia as a practice?

We completed our first spolia project in 1997 and then worked on a project only every two or three years. In the last 10 years we started to do a project annually and now we've got a project here in storage, two other buildings about to be dismantled and we're in conversation about three buildings next year. We’re on an exponential curve of aspirational redevelopment.


Paye are market leading stonework and restoration contractors in London and the South East and are part of the Stone Collective.

All photos by Robert Greer


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