On-going efforts to preserve a landmark historic building in the North-East are revealed in a new exhibition.

Wear and tear caused by centuries of weathering has left guardians of Durham Castle with a permanent problem of conserving the fragile fabric of the Medieval architectural masterpiece.

A display outlining the various restoration and repair projects to keep the Norman-built castle standing safely as a working building opened yesterday.

'Work in Progress - 200 Years of Restoration and Conservation at Durham Castle', can be viewed in the nearby University Library, on Palace Green.

Its centrepiece is a large wooden model, not normally on view to the general public, which opens to reveal the internal lay-out of the designated World Heritage site.

The model was built during major repairs to prevent the castle's west walls literally sliding down the bankside of Durham's central peninsula, in the 1930s.

Since then further appeals have been launched to meet the cost of emergency repair work as new conservation crises are faced by Durham University.

The latest is a round of roof repairs to prevent water leaking into various exposed areas of the castle.

A £1m scheme, backed by the Northern Rock Foundation, it should be completed later in the year, before the worst of the winter weather sets in.

Durham Castle Museum curator, Richard Brickstock, said the exhibition highlights the permanent problem of funding for the university, which inherited the castle when it was founded in 1832.

"The building was handed to the university without any financial foundation," said Mr Brickstock.

"If you give a building to the National Trust they won't accept it unless there's a large financial endowment and the university just didn't have that.

"They can cope with general repairs to patch up wear and tear problems, but realistically they can't pay for the proper upkeep of a Norman castle and so there's a year-on-year underspend."

"Every so often it comes home to roost when a crisis emerges."

The free exhibition, open Monday to Friday, from 9am - 5pm, runs until September 23.