The Co-Operative Insurance Society (CIS) Chief Office was built between 1959-62. Its aim was to provide the company with a headquarters in the north comparable to anything in London. Operating from ten different sites in Manchester following the war, the company wished to consolidate their activities within a landmark building, and took advantage of a bomb-cleared site on Miller Street. The architect was Gordon Tait, of Sir John Burnet, Tait and Partners, who was brought in to collaborate with the already appointed Chief Architect in Manchester, G S Hay.

CIS Tower was the largest office block to be built since the war, reaching 25 floors in height. The design was heavily influenced by a trip to the United States, which resulted in a taller, more centralised building that made use of curtain walling. The brief was for an open plan office building, to house 2,500 staff. The building consists of a striking glass curtain-walled office block, with a projecting mosaic-covered service core. The service core is covered in no less than 14 million one centimetre square, grey tesserae. The mosaic began to fail a mere six months after the building was completed. What was initially a small problem has become an ongoing battle for CIS, who can no longer fix the tesserae back on as fast as they’re falling off. It has become a significant health and safety issue, and hence needs to be addressed.

But how to go about it is another matter. CIS believed it was a question of merely repairing the mosaic – a big job, but manageable. On consulting the experts, they found that their problems were much greater than they imagined, though it must be said not uncommon. The falling tesserae have been attributed to two major problems; firstly, the failure of the tile cement, and secondly, the lack of expansion joints in the concrete, which does not allow for thermal expansion of the mosaic. To re-fix the mosaics would not solve these larger underlying problems, and would therefore mean the mosaic continues to fail. So what other options are open to them? There is the more drastic option of replacing the mosaic throughout, though, of course, with the addition of expansion joints and a thoroughly tested adhesive. The mosaic could be stripped completely and the surface painted or rendered, or the whole tower could be over-clad.

The choice of mosaic to cover the service tower is a key element of the building’s design. The tower reads as a monolithic structure and as a deliberate contrast to the curtain walled office block. Obviously, over-cladding the tower would significantly alter the appearance of the building and a long-term solution that respects the original choice of material would be preferable. English Heritage states that its long-term treatment systems for buildings of special architectural or historic interest must attempt to retain original cladding systems as part of the conservation ethos. However, in a key recent case, Frederick Gibberd’s Liverpool Cathedral of Christ the King, dating from 1967, English Heritage accepted the need to over-clad until research found an answer to the exfoliating mosaic. Unfortunately this has set a difficult precedent.

In the case of the CIS Tower, it appears that the problems can be solved. Because of the nature of mosaic work, there will always be some residual risk of mosaics coming unstuck because of variable workmanship and deterioration of grout, yet this is not sufficient reason to dismiss replacing the mosaic throughout, where the use of the material is a large part of the design, especially in the case of a listed building.

This is, of course, an expensive, time-consuming and disruptive option, which is perhaps contributing to CIS’s reluctance to go down this route. Their favoured option is to over-clad the tower in photovoltaic panels, which, call me a cynic, no doubt earns them brownie points in terms of the council’s reaction to their application. They propose to keep the mosaics in-situ with a wire mesh and over-clad as a temporary solution until a completely successful solution can be found. However, the accompanying Arup report states that it is highly unlikely that any other solutions will become available in the future. The purported temporary measure then gains a much more permanent feel.

If the temporary over-cladding in photovoltaic panels is given the go-ahead it will set down a marker for subsequent cases. The Society’s concern is the extent to which the cladding will alter the appearance of the tower. As mentioned, the current contrast between materials is an essential part of the design. Not only will the photovoltaic panels be blue (currently this is the only colour in which they can be manufactured), but their appearance will be a great deal closer to the curtain walling than the monolithic mosaic tower. There have been successful examples of mosaic tiling being consolidated and repaired, for example at Paddington Goods Yard, a recent Society case. Denys Lasdun’s Grade I listed Royal College of Physicians would also make an excellent case study given that the works carried out here – intensive surface preparation and the introduction of stress relief joints – are similar to that needed at CIS Chief Office, yet this has not been done. The Society is not convinced that installing new mosaic throughout is an unviable option, nor is it convinced that what is being proposed will be temporary.

But the council will be under great pressure to grant permission to the proposals because of the green issues that are intertwined. No one wants to look as though they are unreceptive to ideas of sustainability, and this is a test case that shows that even the world of conservation is not allowed, and should not be, to bury its head in the sand. Yet it is a thorny issue when the character of Manchester’s landmark tower may be altered permanently.

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