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Threadneedle Street
Removal of historic rock
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Over time, the recessed balconies had been covered with historic rock asphalt laid directly onto the Portland stone beneath. While this material once provided a practical waterproof layer, its direct application to the stone posed challenges for conservation. To restore the integrity of the balcony surfaces, DBR undertook the careful removal of the asphalt, working with particular attention to the protection of the historic fabric below.
Because the asphalt had bonded closely to the stone, gentle heat was applied to soften the material. This allowed it to be lifted gradually, reducing the risk of damage to the underlying Portland Stone.
Client
Pacific Oriental
Dates
2009
—
2010
Location
London
Grade listing
Grade II
Fabric
Stone
Preparing the Balcony Structure
Once the historic asphalt was removed, the existing substrate could be properly assessed and prepared for renewal. Care was taken to retain the original screed where possible, ensuring that the new installation would respect the historic construction while meeting modern performance requirements.
Installing a New Waterproof Surface
A new 20mm asphalt layer was installed in accordance with current standards, providing a durable waterproof surface for the balconies. Unlike the earlier arrangement, the new asphalt was fixed to an independent kerb detail, ensuring that the historic stone fabric remained protected and allowing the system to function without placing unnecessary stress on the original structure.
Detailing for Drainage and Protection
To complete the installation, a vapour control layer was introduced around the outlets on the existing screed to manage moisture movement within the balcony build-up. New lead flashings were also installed along the perimeter, creating a secure junction between the balcony surface and surrounding masonry while directing water safely away from the structure.
A Balanced Approach to Renewal
Through the careful removal of historic materials and the installation of a sympathetic modern system, the balconies were returned to safe and effective use. The approach ensured that the historic Portland stone remained protected while providing a durable waterproof solution capable of meeting present-day requirements.
