The dome of Britain’s iconic building had survived the Blitz but Sussex Asphalte had to replace 100-year-old asphalt.
With its spectacular dome, St Paul’s Cathedral is one of Britain’s iconic buildings; the resting place of the nation’s great and good, including Nelson and Wellington, as well as the host of a Royal wedding and a key location for multiple films.
Constructed by Sir Christopher Wren following the Great Fire of London, the building has also survived the Blitz and encroaching developments, but in 2017 the 416sqm of mastic asphalt, first laid in 1906 around the Stone Gallery that encircles the dome, needed urgent renewal after it began letting in water into the gallery and damaging the artwork within the dome.
Contractor Sussex Asphalte Ltd, replaced the failing asphalt with IKO Permaphalt, a polymer-modified mastic asphalt that provides long-term durability, increased fatigue resistance, enhanced temperature stability and carbon neutral properties.
Complexity of the project
The Stone Gallery includes a central gutter covered by iron grills that had to be removed, cleaned and refitted on the new asphalt. To ensure the correct width of asphalt was applied a gutter template needed to be fabricated and used as a guide by the asphalters, requiring skilled precision work. Other detailed asphalt works involved adjustments to rainwater outlets to improve drainage, and vertical upstand into a chase, including a double angle fillet around the Stone Gallery’s circumference.
Successful project management and asphalt installation, in accordance with BS 8218:1998, was key to conserving one of the most important architectural structures in the UK and works had to be phased to enable continued public access to Stone Gallery sections.
Asphalt was stripped and re-laid in sections to ensure watertightness. This enabled the client to view the condition of the Portland Stone paving beneath the asphalt.
The first coat of IKO Permaphalt was applied at 10mm to level out old stone, a second coat was also applied at 10mm and a third coat was applied at 15mm with associated details and solar reflective paint to exposed upstands. Given the conservation and architectural significance of St Paul’s, Sussex Asphalte hosted a site visit by a large group of surveyors to promote the roofing profession and asphalt installation by highly skilled craftsmen.
The Stone Gallery was 53m high and given the sensitivity of the building, it was necessary to create a system of three hoists to ensure materials and waste could be transported on and off site and required careful management. Given the age of the asphalt being stripped, the client was provided the opportunity to view the original exposed Portland Stone. However, the stripping revealed a disused stairwell in the Gallery. After the Clerk to St Paul’s took a photographic record, the void was made safe and
St Paul’s Cathedral remained operational during the works including holding services. Asphalters had to ensure works did not disturb services taking place in the Cathedral.
Taken from the NFRC 2018 Winners UK Roofing Awards Winners Review