Revamp brings new roof to London Hospital

St George's Hospital's Jenner Wing undergoes improvements including application of a cold-applied liquid waterproofing membrane roofing system

St George’s Hospital’s Jenner Wing has undergone a major revamp, including application of a new cold-applied liquid waterproofing membrane roofing system.

Led by Hunters Architecture, the project was delivered across Block D of the Jenner Wing by contractor Mitie Roofing using Kemper System’s solvent-free Kemperol 2K-PUR solution.

Paul Butler from Mitie Roofing said of the scheme: “There is a significant amount of air handling equipment on the roof to serve the ventilation services.

“This not only meant that the equipment needed to remain operational throughout the roof refurbishment, but also that the scheme must not involve any nuisance odours that could cause disruption to patients, staff or visitors.”

Both the primer and the resin used to install the membrane have a solvent-free, odourless formulation and the membrane is installed in a single process without any need for hot works. It can also be applied to match to the exact contours of the many upstands on the hospital roof.

The total roof area of Block D is more than 1700sq m, so the project was divided into two phases; with 940sq m of membrane installed in phase one, followed by the 819sq m during phase two. Both phases were installed as an overlay onto the existing asphalt roof.

Before each phase could begin, Mitie had to prepare the roof area. Lifting equipment was used to raise the air handling plant on the roof and this was supported on rubber feet. The loose chippings on the roof were then removed by a mechanical scrabbler to prepare the surface for the overlay of the new membrane.

However, in areas below the air handling plant where the machine could not be used, this process had to be carried out by hand.

Around the perimeter of the roof there is a railing that supports the basket used for window cleaning and, inside this, the roof is covered with paving slabs, which had to be removed in order to install the waterproofing membrane underneath. With the slabs removed and set aside for re-use where possible, the installation team cleaned the surface using jet washing equipment prior to application of the primer once the roof was dry.

The Kemperol 2K-PUR resin was then applied in a single wet-on-wet process in which the resin is first applied to the substrate; reinforcement fleece is then laid directly on to the wet resin, immediately followed by more resin on top. This ensures complete saturation of the reinforcement fleece.

Once cured the resin forms a seamless, elastomeric waterproof membrane that cannot delaminate, is UV stable, and bonds directly to the substrate.

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