EXPERTS have revealed that hundreds of extra stones will need to be replaced after damage Truro Cathedral's iconic spire was discovered to be worse than predicted.

Working in perilous conditions stonemasons have been steam cleaning the Bath stone while perched more than a hundred feet up on scaffolding that is due to reach the spire's tip - 245ft up - by the end of the month.

The specialist cleaners are scrubbing away years of grime to reveal crumbling stone - eroded by the county's salty atmosphere and biting winds.

Stuart Aston, managing director of WR Bedford, the South West based firm contracted to carry out the cleaning and restoration work, expected to take nine months, called it a once-in-a-lifetime job.

"This is such a prestigious job and one that is unlikely to happen again in my lifetime," he said, adding that 1,200 stones had initially been marked for replacement or repair - but now that figure is nearer 2,000.

The sheer scale of the project is illustrated by the fact there are 25 miles of scaffolding tubes, eight miles of wooden planks and 30,000 fittings (clips attaching the tubes).

Pointing to black grime on the stone face as the West Briton scaled the scaffolding's heady heights with him, he said: "You can see the pollution has built up creating a hard crust on the stone. Water has seeped in behind it crumbling and cracking the stone."

In places the damage is so great that the stone resembles honeycomb.

"It's important that we are here now, potentially the stone could have collapsed because it has been weakened by the damage."

This is the first clean and major restoration of the central Victoria spire, named after the queen in commemoration, since it was constructed in 1905.

Stonemason Mark Cole, 43, from Trispen, was replacing the Bath stone with Syerford Stone considered to be a stronger alternative, despite a fear of heights.

"My family has made fun of me because they know I hate heights, but you just focus on the work in hand. I've been up here two weeks now and I'm getting used to it," he said.

There will be up to 12 stonemasons working on the cathedral. It takes them about one day to carve out one piece of stone and then chip out the old stone to replace it - a painstaking job in challenging conditions.

The restoration is part of a £4 million Inspire Cornwall project to preserve the cathedral, create a green city oasis in its garden and establish an educational, music and art centre.

So far 800 people have sponsored a stone in the Save Our Spire (SOS) campaign raising a staggering £45,000. 60% of the donations have come from Cornish people.

"It is difficult to raise funds of any kind in the current climate, we are extremely pleased with the campaign so far and the generosity of the Cornish people, said a cathedral spokesman.

Full details of the scheme are available from the Appeal Administrator at the Cathedral Office 01872 245013 or from the Inspire Cornwall website www.inspirecornwall.com

To see the slideshow click here.