"A slight crack appeared in the cornice of the ceiling in the Reading Room just after Christmas and the library decided to start repair work immediately as a precautionary measure, " said a National Library spokesman.

The library's already extended opening hours will continue as normal but, as scaffolding is in place, Reading Room services and microfilm facilities have been moved to the firstfloor landing while the repair work is carried out, the spokesman added.

The repair work to the historical building, which flanks the DA il at Kildare Street, will take about six weeks, and readers should be able to return by the end of March.

Though unrelated to the crack in the ceiling, refurbishment and cleaning work on the outside of the building will continue while the Reading Room ceiling is repaired, said the spokesman.

"Heavy drilling work associated with the refurbishment is restricted to early morning and weekends so as not to disturb the readers."