A part Lottery funded £41m project to restore the London Coliseum has chosen Non Destructive Testing methods to investigate the hidden structural features within the impressive façade of the historic building.

The celebrated Grade II* Listed building stands in a prime location overlooking Trafalgar Square. It has been one of London's landmarks since its opening in 1904, and was in desperate need of repair and renovation. The building has been home to English National Opera since 1968 and the company has embarked upon a programme of restoration and essential works with the intention of restoring the theatre to its former glory by its centenary in 2004.

The survey conducted by Aperio, specialists in Non Destructive Investigation came about as part of ENO's mission to repair and restore the cracking terracotta façade. The survey was required to identify the presence and vertical extent of steelwork built into the façade and in selected columns of the front of house area. Information on the location and depth of additional metallic inclusions was required in order that any current or future corrosion leading to cracking of the façade could be addressed.

The Aperio team carried out the comprehensive survey over six days after an initial evaluation in which a range of Non Destructive techniques were trialled. A combination of the two methods was adopted as the most effective way to collect the information and these were an advanced digital radar system to provide information on the metal work within the walls, whilst Elcometer P330 digital cover meters and metal detectors from Oxford based company Protovale, were used to locate metallic objects embedded in the façade.

An Elcometer P100 and Elcometer P120 were used to provide a rapid method of locating metalwork within the façade to a depth of approximately 400mm. A Protovale P330 Covermeter was then used to determine the approximate depth of the features identified.

The main steel columns supporting the tower were found to be continuous whilst other columns added at a later date were found only at certain floor levels. Exposures previously opened up on the façade were used to calibrate the data.

Aperio offer a range of Non Destructive inspection and test options for the investigation of historic and modern buildings, structures and sites. The team has over a decade's experience gained in working on the royal palaces, monuments, cathedrals and castles in the UK and overseas.