Like every business with unique and proprietary products, it is difficult to exalt the benefits unless thorough testing and a track record is available. The following details the story behind the testing and eventual project that helped cement the Screed Replacement Tile (SRT) as the best alternative to screed. The information from the tests undertaken and subsequent results have never been published, until now.
In 2010, JUPITER were approached by the architectural practise Wilkinson Eyre. They were considering the use of the unique JUPITER underfloor heating system within the refurbishment of the New Bodleian Library in Oxford. The library was designed by Sir Giles Gilbert Scott and constructed between 1937 and 1940. Wilkinson Eyre were appointed to design and modify the building internally to provide improved storage facilities for rare and fragile material, as well as better facilities for readers and visitors. The library reopened in 2015 as the Weston Library.
The design team was keen to reduce the mass and height of any proposed underfloor heating system over the new floor slabs. Rather than using a traditional screed, the SRT system was considered for its extraordinary performance under stone floor finishes. Although the system had already been used on countless projects both in the UK and Germany, the design team wanted scientific evidence that the system could provide a robust substrate for the chosen stone floor finish.
Stone consultants, Harrison Goldman, were appointed by the client to oversee the detail of the stone floor installation and it was Harrison Goldman that suggested a full-scale deflection test was conducted to demonstrate empirically the capabilities of the system.
Therefore, in February 2011, JUPITER commissioned the Building Research Establishment in Watford to undertake a full-scale deflection test based on the proposed 8 m span concrete slabs. A large 64 m² model was constructed to simulate the proposed build-up, comprising JUPITER Ideal EPS heating panels, the SRT system and a 600 mm x 600 mm x 20 mm Moleanos limestone finish on a flexible adhesive bed.
The test rig consisted of main steel girders with cross steels and a ply structural deck. The main girders were supported on hydraulic rams to bring the initial structure to exact flatness (zero deflection). The ply deck was then covered with the JUPITER Ideal EPS heating system and SRT system.
A further, elaborate rig was then set up over the test construction to simulate an imposed load and to force the floor structure to deflect. This downward force was introduced using further hydraulic rams.
The initial release of the supporting hydraulic rams causes the total structure to drop significantly without showing signs of cracking within the stone floor or joints. The hydraulic rams above were then used to force the floor construction down gradually to 32 mm below the position of zero deflection (the equivalent of the span / 250). Only then did a small hair line crack appear within the joint line of the installed stone finish.
The BRE team summarised the results as follows:
‘These deflection tests appear to have demonstrated the ability of the JUPITER floor to accommodate appreciable vertical displacements of the supporting structure through a mechanism that enabled the various layers (e.g. insulation, SRT) within the floor to act as unbonded sliding supports. This sliding mechanism prevented the substantial deflection of the substrate inducing large tensile stresses in the brittle and comparatively fragile limestone tile finish.
These tests have indicated that the JUPITER Floor system (JFS) is able to accommodate vertical downward mid-span deflections of the substrate up to a maximum of 32 mm (L/250) before cracking and/or local damage becomes evident in the grouted joints to the stone finish.
The ability of the JFS to move relative to the structural floor substrate by acting as a sliding support to the floor finishes enables the JFS to accommodate deflections more than the maximum deflections of L/720 quoted in the Stone Federation Guide.’
It has been nearly ten years since the floor at the Weston Library was installed and there have been no reports of any problems with the stone installation whatsoever. Since then, many thousands of square metres of SRT have been installed and not a single crack or fracture has occurred in any of the stone or tile finishes that have been installed.
More project information can be found on the Wilkinson Eyre website.
More information on the Screed Replacement Tile system can be found here.