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Mike Smith Studio was commissioned to undertake a Research and Development study to ascertain whether it would be possible to produce a replica of the empty fourth plinth in London’s Trafalgar Square for Rachel Whiteread. The replica was to be produced in water-clear polyurethane resin, and would measure 5 metres long by 5 metres tall by 2.5 metres wide and weigh 11 tonnes. The R&D would identify all aspects of the project; site survey, local authority permission requirements, material sourcing, mould design, structural engineering, construction, transportation, installation, budget requirements, time scale. The challenge was to produce the largest ever cast polyeurethane object.


Since a turn-key solution was required MSS was responsible for the management of the complete project. The focus of the first phase of management was Research and Development, in particular finding the material that would work on this scale. Various resin manufacturers were consulted and after choosing one, a testing program was developed in order to ascertain if the material would meet the demanding requirements the project would impose on it. After conducting the testing and selecting the material we proceeded to construct the moulds, pour the resin, repair and clean the cast, and finally install the piece to time and budget schedules.


The demands of the project required highly creative solutions. The material would start out as a low viscosity liquid and transform to a solid via expansion and contraction, rising to a temperature of 130 degrees centigrade. The pressures created in the mould could cause unsatisfactory distortions in the final casting unless the design of the mould could control and rectify them. Material shrinkage had to be taken into account, so that the finished castings were the same size as the original granite plinth on which they would sit as a mirror image. These castings had to perform structurally at such a scale. An analysis carried out by acredited structural engineers was therefore incorporated into the mould design. Finally the moulds were designed in such a way that they could be assembled and removed in parts. Lifting frames were also designed for the two sections to be installed in position in Trafalgar Square.


The casting was very complex due to the demanding nature of the material and required the fabrication of two inner and two outer moulds. After several test castings it was determined that aluminium would best suit the fabrication of these moulds due to its thermal conductive properties which also gave an excellent surface finish to the resin. Rubber gaskets were used for sealing the sections of the inner moulds. The fabrication of the outer moulds involved considerable and complicated folding and forming of the aluminium extrusions in order to replicate all of the decorative details of the original plinth. Mild steel was chosen for the structural work surrounding the outer moulds and for the internal hydraulic jack mechanism because of its strength.


The restrictions imposed by the local authority with regard to working on a listed monument made the installation of the work more complicated then it would have been otherwise. Scaffolding had to be erected around the granite plinth for safe and precise alignment of the two cast sections. The installation could only take place between midnight and 8:00 am because the road surrounding Trafalgar Square had to be closed to allow for crane access. Crowd control barriers were put in place to deny public access during the installation process. This procedure was repeated six months later for the removal of the sculpture.