Since opening in 2002, the £30 million museum has far exceeded its expected visitor numbers. A key feature of architect Daniel Libeskind's outstanding design is the use of materials in their raw form.
Mastic asphalt was chosen for the 3,500m 2main exhibition floor. Designed to represent the surface of the earth, it is gently curved in all directions, rising to a 'North Pole'delineated by a metal cross set into it at one end. Lines of latitude widen apart as they progress away from the pole.
'There were various criteria in selecting the flooring, 'says Leach Rhodes Walker's project architect David Baxter. The surface had to be capable of taking the load of large exhibits such as army tanks. 'The floor is also heated, and there are pipes within it, so we wanted a material that would be sympathetic with that, and we also wanted a smooth surface, so it had to be a trowelled or applied finish rather than tiles. But one of the overriding factors was the very strict budget for the project.'
'The material was laid in bays with the bay sizes dictated by the lines of latitude, starting at the highest point, the North Pole, ' explains Steve Percival of Briggs. The longest pour - where the lines were furthest apart - took six hours to lay. 'It went down on top of a concrete floor that had been laid to the curve, but we had to put a regulating layer down before the surfacing layer to get it to the right levels.' A final check showed the floor had been laid to within a tolerance of ±2mm.
The architect wanted a light finish to reflect film projections - an effect that was achieved by dressing the surface with fused alumina particles. The lines of latitude were delineated by polishing the mastic asphalt instead, to give smooth, dark lines.
Project: Imperial War Museum North, Manchester
Client: Imperial War Museum
Architect: Studio Daniel Libeskind/Leach Rhodes Walker
Main contractor: Sir Robert McAlpine
Mastic asphalt contractor: Briggs Roofing & Cladding
Mastic asphalt supplier: Permanite