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Case study: A seven-deck multi-storey car park above a retail area in Horsham, West Sussex

The building is a precast-concrete structure of beams spanning 15.6m, with precastconcrete planks laid in between, finished with a 75mm structural concrete topping.

The first two decks are above the retail space, and a 50mm mastic-asphalt waterproofing layer has been installed to prevent water ingress into the shops below.

The top two decks are open to the elements and a 30mm layer of mastic asphalt waterproofing has been applied.

'Mastic asphalt was primarily chosen because it is a standard product with a good history, ' says Chetwood's regional manager Paul Hunter. 'It's also very hard-wearing, which made it suitable for parking areas. We would expect to get a 25 year life from the material, and the maintenance regime should be simple.'

Responsibility for maintenance will be handed over to the local authority once the development is complete.

'We have used our tried-and-tested Flexiphalte deck waterproofing system, ' says Rock Asphalte's Bill Ashley. The company has used the polymer-modified product on more than 250 deck applications, including the car parks at the Bluewater and Meadowhall Client: Sainsbury's Architect: Chetwood Associates Main contractor: Carillion Building shopping developments.

Rock Asphalte pioneered the development of polymer-modified mastic asphalts in the mid-1980s, and was also one of the first companies to introduce hot charging for laying large areas of paving and roofing - now standard procedure throughout the industry.

The Horsham contract involves laying approximately 6,000m2 of Flexiphalte across the two lower and two upper decks of the seven-deck car park.

Project: Multi-storey car park, Horsham

Mastic asphalt contractor: Rock Asphalte

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