Sample terracotta blocks produced by manufacturer CeraFrance are understood to have failed structural engineering tests. The trials were commissioned by Building Design Partnership, architect and structural engineer on the lottery-funded project.
A source close to the project said the hollow terracotta blocks, which were supplied by London-based firm In Situ, failed compressive strength tests three weeks ago and only passed when filled with concrete. Eight thousand blocks are to be used in the south porch of the Victorian concert hall.
Consultants and contractors have expressed concerns about these results. One said: “Terracotta should not rely on infill material for its strength. Terracotta expands over time and concrete shrinks so the terracotta itself should be structurally load bearing.”
BDP was due to submit final samples of terracotta to English Heritage in early autumn for approval but the architect confirmed that CeraFrance had yet to produce them.
Traditional manufacturers, such as Shaws of Darwen, Lancashire, and Ibstock Hathernware of Loughborough, make their blocks by pressing the clay into the moulds by hand and taking regular measurements. CeraFrance has developed a cheaper process in which, it is understood, liquid clay is poured into linked moulds.
The conditions of the listed building consent require English Heritage and Westminster council to check that the colour, texture and profile of the terracotta blocks match the rest of the building.
John Fidler, head of architectural conservation at English Heritage, has also expressed concern about prototype blocks presented six months ago, which were 12-15 mm thick, instead of one inch. He said: “Discussions are going on about the samples to be submitted for the terracotta. There are issues to be resolved. The challenge is always to get materials that match. I believe that the colour and texture of samples is improving. If it does not look like the original, it may not get listed building consent.”
Martin Ward, project director at BDP, denied that it awarded the contract to CeraFrance, via In Situ, simply because its quote was cheaper. He said: “It was a balance between the price and making sure it was the right technical proposal.” A UK representative of CeraFrance said: “The manufacturing technique is a response to issues in the brief.”
Works on the Royal Albert Hall are due to be completed in early 2000.