The normally quiet upper part of Merchants Street in Valletta was buzzing with activity yesterday as men in fluorescent shirts climbed up and down newly-erected scaffolding on one side of Auberge de Castille, the office of the Prime Minister.

They were preparing the way for workers from the Restoration Unit to start painstakingly removing the grime that has accumulated on the walls of the majestic building over the years.

The restorers will start work on Monday and it is expected to take them until 2012 to finish the job on all three sides of this majestic building which, when considering the elaborate sculptured decorations, span some 6,000 square metres in all.

This will be the first time the 16th century auberge, built by Grand Master Manuel Pinto de Fonseca, will be properly restored, Norbert Gatt, one of the architects in charge of the unit, said. Some minor works had been carried out after the building was hit during World War II.

Pointing to the blackened walls, Mr Gatt said this damage was typical of the area, which for years has been pummelled with pollution from the power station and from passing cars.

And the close proximity to the sea does not help, with the salt causing the stone to deteriorate. The sculptured parts were even more damaged since the stone used was softer and more susceptible to erosion, Mr Gatt said.

Although he could not give an exact estimate of the cost of the works, the architect said the whole project was expected to run into a couple of tens of thousands of euros.