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Maintaining any building can be a tough challenge, but when the landmark building in question is also open to the public, visited by VIPs from around the world, and in constant use, those challenges are magnified.

Guildhall is just such a building. Home to the City Of London Corporation, some sections of the building date back 800 years, and it still provides a base for council services and a venue for state banquets and corporate events.

One of Guildhall’s most treasured resources is its library and archive, which specialises in the history of London. A more recent addition, opened in 1974, its distinctive interior is echoed on the roof, where 56 pyramid roof lights make it instantly recognisable against the skyline. A recent project to refurbish the roof had to take account of the unusual roof design and Kemper System’s Kemperol 2K-PUR liquid waterproofing system was chosen to accommodate both the complex detail of the roof features and satisfy the operational and sustainability needs of Guildhall’s management team.

Flexible System

Kemperol 2K-PUR, is Kemper System’s solvent-free wet-on-wet membrane, which is based on a castor oil resin formulation derived from sustainable crops. The liquid resin is applied with a non-woven, flexible reinforcement fleece manufactured using a 25% recycled plastic bottle content to create a durable waterproof membrane that can follow the exact contours of any roof. That meant that Kemperol 2K-PUR was a simple-to-install product that formed a permanent bond to the unique features of the Guildhall Library roof, with precision application to the pyramid roof lights’ upstands and drainage channels, which are located extremely close together in the central roof area.

Other advantages for the City of London Corporation included close alignment to the corporation’s environmental aims.

Explains Michael Coleman from the City of London Corporation: “Choosing a solvent-free and odourless cold-liquid applied system meant that we could continue on a business-as-usual footing without having to worry about fumes or the hazardous equipment used for hot-applied systems. What’s more, with a BBA certified service life in excess of 25 years, we can be confident that our investment in refurbishing the roof now will serve for a long time to come.”

Business as Usual

The brief to roofing contractor, A&L Roofing Services, was to complete the project within a six week programme, during which the library had to remain fully operational. The installation team began by cleaning and preparing the asphalt surface which had begun to blister and split. Kemper System’s Kempertec primer was then applied to stabilise the substrate and provide a chemical key for the waterproofing resin. Once this had cured, the Kemperol 2K-PUR waterproofing membrane was installed onto the roof. Applied in a single process, the Kemperol resin saturates a non-woven reinforcement fleece and cures to form a monolithic membrane without laminations that is UV stable, extremely tough, flexible and tear resistant and bonds directly to the substrate.

The reinforcement fleece was cut to size and shape on site to enable the meticulous detailing and protection of the most vulnerable parts of the roof around the roof lights, outlets and upstands as well as the flat roof areas.

Lee Lane from A&L Roofing Services comments: “Keeping the library open during the six week programme meant that the old rooflights had to remain in place while the job was done before being replaced with new pyramid rooflights at the end. This made for a very challenging project which could really only be delivered by a cold-liquid applied system that can be applied accurately to the multiple facets and contours of the complex detailing.”


Specification of Kemper System’s Kemperol 2K-PUR on the Guildhall Library roof followed use of the system during the refurbishment of the west wing, which sits above committee rooms and accommodation for high ranking councillors. This 1,200m2 section of the roof is similarly complex with architecturally striking features and numerous service units and was refurbished by specialist contractor CRC Group Ltd in a 10-week programme.

Explains Steve Webb from CRC: “The west wing roof is concrete with a bituminous felt surface incorporating an aluminium facing and it had started to present a risk of leaks in some areas. One of the key advantages of the Kemperol waterproofing system is that it can be overlaid onto almost any substrate which dramatically reduces the amount of waste that would need to be removed to landfill and the preparatory work involved and therefore minimises the time required on site.”

Stuart Hicks from Kemper System adds: “Kemperol 2K-PUR provides the ideal waterproofing system for installations like Guildlhall where the roof is full of complex detailing and the building’s occupier has both a strong environmental commitment and an operational requirement to keep the building open throughout the project. For both of these Guildhall projects the absence of any nuisance odours was a significant advantage and, thanks to the system’s durability, it will be watertight and be able to withstand footfall from maintenance foot traffic to service the plant on the roof for many years to come.”

Reader Reply Number 165027
Kemper System
t:: 01925 445532

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