More than a century of city grime has been removed from Marble Arch, one of London\'s most famous landmarks, in a three-month restoration project headed by English Heritage and carried out by David Ball Restoration (DBR).

The clean and repair project to the 13.7m tall Carrara marble monument included repointing of masonry, reinstating broken and missing detail, bronzing the gates and lanterns and installing pigeon proofing. The cost of the project was £75,000 - just £5,000 less than the cost of originally building the John Nash arch in 1828.

Traffic pollution had been a major contributor to the build up of grime on the monument since the 1900s and especially since road realignments left the arch stranded on a traffic island at one of the capital\'s busiest junctions.

More recently, acidic pigeon guano has also been soiling the fresh appearance of the Carrara marble and accelerating its decay.

David Ball Restoration first became involved with the project in 2003 when they carried out pigeon deterrent system trials on the Bas reliefs to the south elevation. Complete conservation followed.

"The first challenge was to remove the guano deposits safely and quickly," says Brendan Foley, DBR\'s contract manager. "This was done by manually scrapping it away with plastic spatulas. "When the deposit was removed we were able to clean the stonework, using nebulus water mist to lift the surface pollutants. The Doff cleaning system was also used in some projecting cornices to remove organic growth and staining."

In the subsequent survey of the clean stonework, many poorly executed earlier repairs were identified, in particular indent repairs using mortar rather than marble. All of these were cut out and replaced with Carrara marble.

Many corner details and moulded bands on the base of the Corinthian columns had been damaged and these, too, were replaced with new stone. Open mortar joints, some in prominent areas along the top, needed to be treated and repointed, as did cracks in some of the larger and heavier stones revealed by the cleaning.

These cracks are thought to date back to 1851, when the Arch, which was built as the grand entrance to Buckingham Palace, was dismantled and re-erected where it now stands.

While DBR worked on the stonework, subcontractors restored the bronze tipped processional gates - once the largest in Europe - and repaired and repainted the lanterns that illuminate the monument.

"The Arch is looking A1," says Christopher Cooke of English Heritage who directed the project. "Routine annual maintenance will keep it looking that way and we\'ll make another inspection in five years to check that the pigeon deterrent system is still protecting the fabric. I don\'t think we\'ll need to revist the repointing or cracks in the stonework for a good long while.""