City Hall, Bristol

Bristol City Hall is a Grade II listed building on College Green and remains the civic heart of the city. We repaired, waterproofed and resurfaced the building’s two main entrance ramps, conserving and reinstating the historic feature flagstones that frame them.

The brief

The ramp surfaces had failed, and the concrete deck beneath, which sits directly above plant that powers the building, needed a new waterproofing system. The stone flagstones lining each ramp are a defining feature of the entrance and had to be retained. The package combined heritage stonework with deck waterproofing and asphalt surfacing on a live, publicly accessible civic building.

What we did

• Surveyed and recorded the position and orientation of every feature flagstone before lifting, so each could be returned to its original location and pattern
• Carefully lifted the flagstones and removed them off site for specialist cleaning and sealing, replacing any beyond repair with carefully selected matching stone
• Broke out the failed asphalt and weak lean-mix concrete down to the sound substrate, with noisy breaking out carried out at weekends and out of hours to avoid disturbing occupants
• Applied a liquid-applied waterproofing membrane to the prepared deck, turned up and bonded to the stone channels either side, with integrity testing before resurfacing
• Laid new Tarmac Ulticolour coloured asphalt to the required falls, then re-laid the cleaned flagstones on a mortar bed to the original pattern
• Sealed all joints with colour-matched sealant, renewed the channel white lines, reworked the fire hydrant chamber and cover, and removed, stored and reinstated the cycle racks on shallow fixings that do not penetrate the new membrane

The challenge

Because the deck sits over plant serving the building, the exposed concrete had to be made watertight at the end of each shift, by permanent membrane or temporary covering, so nothing below was ever at risk. Every flagstone was handled to protect its surface and arrises so the finished ramps matched the original.

The outcome

We handed back two fully waterproofed and resurfaced entrance ramps with their historic flagstones conserved and reinstated, delivered on time and within budget around a live building with public access maintained throughout.