The ACT government shut the library in May to replace water-damaged walls and investigate the possible presence of asbestos, which was found in bonded sheeting in the ceiling but declared safe if undisturbed.

The library partially reopened in July, with a large section boarded up to allow works to fix damage from a wet weather event to be fixed.

The works included the replacement of some flooring and improvements to subfloor ventilation.

In a statement on Thursday, the government's city services directorate said asbestos had been found in "inactive bathrooms" in the subfloor. The bathrooms were not accessible to the public.

The statement said a full closure of the library, starting on Friday, September 28, was necessary to have the material safely removed.

"Like most buildings built before 1990 in Canberra, materials containing asbestos were used in the library’s construction," it said.

"The library has an asbestos management plan in place and these materials are safe if undisturbed."

While the library is closed, the government is encouraging people to instead visit branches in Civic, Gungahlin and Belconnen, which are operating as usual.

Return and request dates will be extended to October 5, with return chutes closed.

Alternative arrangements are being made for people who have booked a community room at Dickson Library.

Library members can also search for, reserve, renew or download items online at www.library.act.gov.au.