Renovating with Roman cement

Renovating with Roman cement

Master plasterer Phil Bailey and the team at Triskele Conservation tell Professional Builder about a renovation using Roman cement.

What did the Romans ever do for us? Well, when it comes to Roman cement, not a lot, as it happens, because the moniker is actually somewhat misleading. The material was, however, a ubiquitous feature of London facades from its development by one Joseph Parker in the late eighteenth century, until it was overtaken by the emergence of Portland cement in the middle of the nineteenth. Phil Bailey is one of its modern masters, and Professional Builder caught up with the expert building conservationist at a property that, just like Roman cement itself, has been brought back to life.

Before successive waves of gentrification would break across our capital many of its boroughs were rather less salubrious than today, but few individual properties could have declined quite so dramatically as a once imposing 1850s address in Stockwell. Its elegant, Corinthian-style façade scarred with graffiti, and the interior behind a home to new ed drugs dealers and local gangs, a devastating arson attack in the mid-1990s would then leave it little more than a shell, with no floors and little roof remaining. That was before the intervention of Jessie Mills and her then husband, when they acquired what had been reduced to a sorry relic of a much grander age at auction.

“The accommodation is arranged over three floors but when we bought it you could stand at the lowest level and look up to see nothing but sky, and charred timbers,” she recalls. “That was in 1996 and it would take us three years to make it habitable. Our intention throughout the project has always been to remain true to the original building techniques. That’s why we’ve used lime plaster throughout, for instance, and rebuilt authentic wooden shutters for the windows.” Not only that but externally, Jessie would remove much of the sand and cement pointing herself, and replace it with a lime mortar, but the decorative detail in the architraves would require more skilled hands.

“Roman Cement was only given that name because the Victorians thought it resembled the monumental architecture of the ancient world,” explains Triskele Conservation’s Conor Meehan. “In reality it is actually a mixture of clay and calcium carbonate, which is found in combination in naturally occurring septaria stone. The Holy Grail in the building boom of the industrial revolution was a material that would set under water, and that’s just what Roman Cement provided, and it would first find its place in lighthouse construction as a consequence. Back then it was mined at locations around our shores, but eventually they were using so much of it that it was damaging the British coastline. That and the introduction of Portland cement would lead to its demise.”

Rather than simply remove what was left on the façade, Jessie was determined to retain as much of the original as she could, and she found a kindred spirit in Phil Bailey, who has painstakingly repaired and replicated the work of his nineteenth forebears. “The material we use is sourced from a French company called Vicat, and I have my own mixes that I have found work for us. Just like lime, it has exceptional vapour permeable characteristics, which allows the building beneath to breath, and won’t trap moisture against bricks or the timbers. It is far more flexible and elastic than any modern equivalent, and is a lovely material to work with, but very fast setting, so managing it is the real skill.”

It is a testament to the durability of Roman cement itself that it has survived treatment that would be more reminiscent of a war zone than a residential London street, but survive some of it did, and that has provided Phil and his team with a template that they can replicate. He first makes rough moulds in plywood from what is already in situ, with zinc plates then fixed to them to reproduce the finer detail. Once the newly mixed Roman cement is applied, the moulds are run along the length of the architraves and, with the zinc cutting through the material, it leaves an authentic companion to the original in its wake.

“We certainly don’t want to be removing anything that can be saved and, at the same time, we don’t want to try and hide the fact that it’s been repaired,” continues Phil. “Piecing in the new with the existing can cause problems, because there are always areas you didn’t legislate for, but we see it as the right approach. Where some people would produce the architraves for a project like this one off-site and then fix them to the building, I can be confident that our on-site approach doesn’t differ fundamentally from practices that are centuries old.”

The Stockwell property demonstrates a very typical use of Roman cement and, whilst many tradespeople of today might be unaware of its use, it can be found across the capital. Adds Phil: “The type of mouldings on this property follow a pattern that you’ll find all around London. There are rectangular blocks known as dentils, for instance, and whilst they might be decorative they would serve a practical purpose in drainage and water transportation from the facade. With this property we were fortunate enough that some of the more intricate lion’s heads and rosettes were found just lying around the garden. We can pour silicone over these to create a mould, and with that you can cast as many of that shape as you like. Because it goes off so rapidly, you can then take it out of that mould in minutes.”

“It’s all about using the right material for that project,” concludes Phil. “On a building of this age, with single skin brickwork and lime mortar, you can only ever use a lime or Roman Cement on the exterior. If you do that, then what we added will last for just as long as what was already in place.”



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