Specialist stonemasons have begun the process of removing the stone piers between the windows on the west wall of the building, research to source replacement timber is well underway and specialists have begun the painstaking job of re-assembling the 600+ fragments of the original lights which were retrieved following the archaeological survey.

Though around 90 per cent of the grade A-listed building, which was completed by Charles Rennie Mackintosh in 1909, was saved, the library was almost entirely destroyed in a fire in 2014.

Within the library itself, a forest of steelwork is securing the external structure before two massive stone window piers are removed for assessment. The steelwork alone took three months to erect, with two weeks spent tightening over 900 bolts.

Detailed surveys of the existing stone library piers to determine the exact amounts and sizes of stone needed for repair have been already undertaken. The library windows, the frames and glass, have been removed and stitch repairs to the lintels above the windows to strengthen the section in advance of further works has been completed.

The important and complex work to remove the two stone window piers on the west elevation of the building involves a number of stages, processes and expertise to complete, though a decision to remove both piers simultaneously, instead of the initial plan to do one at a time, has saved time on this particular stage.

During the fire, the building’s stonework endured temperatures in excess of 1,000 degrees centigrade and was then cooled down very quickly by the fire brigade. This has quite possible damaged the stone, therefore specialist stonemasons are taking each layer out, assessing each of the individual stones and then either replacing them completely, replacing them in part with new stone indents, or retaining the best preserved and structurally intact of them.

“After months of preparation and detailed research work with the design team we are excited that the restoration work is now underway,” said Liz Davidson, senior project manager for the Mackintosh Restoration. “The current work will enable us to establish how much to the original stone from the library piers can be re-used in the restored piers.”

“The heat of the fire in the library shattered and fissured the stonework making some of it too weak for reuse. As each stone is removed from the piers we are checking to see whether it is strong enough to be reused. Our main focus is in retaining as much as possible of the external stonework with its highly skilled tooling and subtle carved profiles – at each layer we will attempt to save and protect these facing stones whilst strengthening the piers from within.”

Kier Construction Scotland was appointed in June to provide full construction management services to deliver the entire restoration project, beating off another four firms invited to tender. The design team is being led by Page/Park Architects.

One of the key commitments that the GSA sought from its main contractor is supporting the creation of a range of specialist craft apprentices.

Gordon Reid, business development manager at Kier Construction Scotland, said: “Kier has a wealth of experience delivering internationally important heritage projects. This expertise and transfer of knowledge to our site team is crucial on a restoration project like this, as we carefully blend traditional craft skills with modern engineering and state-of-the-art technology.

“We are currently replacing the stone in the library which has been significantly damaged in the fire. This will involve cutting new stone to the rough dimension of the old stone with modern tools before our craftsmen use hand tools to expertly finish the new stone to replicate the original stone.

“Throughout this project we will be working closely with the GSA, local suppliers, specialist conservators and craftsmen, local artists to provide specialist training, apprenticeship and employment opportunities on the project. Stirling Stone has specifically recruited a first year apprentice to work with them on the stone restoration of the project and developing intricate hand tooling skills will be a significant part of this training. This unique project provides a fantastic opportunity to develop the next generation and help to address the construction skills gap in Scotland.”

Ross Dunn, a stonemason working on the project, described how important the work is to his career and his professional interest.

He told Scottish Construction Now: “As far as intricacy goes, it isn’t the most complex building I’ve ever worked on but it is unique because Charles Rennie Mackintosh’s distinct design makes it stand out. It is an interesting job for a stonemason to work on and being from Scotland I can take extra pride in being part of something that is world renowned.

“Conservation is what I am interested in. I’ve done modern masonry but it doesn’t have the same gratification that this does.”

One of the many things that the restoration team have learned from their research into the library is that the material used was Tulip wood which had been imported from the USA.

“At the moment we are looking into a number of possible sources in the USA for the replacement timber and hope to pin this down in the coming weeks,” added Davidson. “One of the major differences that people will notice on visiting the restored library will be the colour of the wood. It will be much lighter than it was in 2014 which been darkened by over a century of use.

“The original timber was lightly stained to allow the grain of the wood to clearly show through – Mackintosh maintained this approach to the honesty of the materials he used throughout the building and it is an approach we are committed to honouring in the restoration.”

The library will also be much more sparsely furnished. After much detailed research the design and restoration teams decided that it should be returned to its 1910 configuration removing many of the later accretions including additional bookcases and the internal staircase. When the library reopens access to the mezzanine level will once again be through the original door on the half landing.

It was also revealed yesterday that work has begun on the painstaking reassembly if the hundreds of fragments of the original lights that were retrieved from the library after the fire.

“It’s taken a year of work by the restoration team with our colleagues from Archives and Collections, to develop our conservation methodology and sort the light fragments into light ‘kits’,” explained Sarah Mackinnon, project manager for the Mackintosh Restoration.

“These are now being transformed back into complete lights by Rodney French of Lonsdale and Dutch in Edinburgh.

“We have enough fragments for 29 complete lights and a minimum of a further seven which will incorporate original and new parts. We need 53 lights to reinstate Mackintosh’s original scheme, the missing lights will be reproduced from scratch by Rodney. This work will be completed by late 2018.

“The decision by GSA to undertake an archaeological extraction of fragments from the library has made the restoration of so many lights possible and the work of Kirkdale Archaeology and AOC has been vital to the practical restoration work now underway.”

Restoration of the Mackintosh building is expected to conclude in time for undergraduate students to have use of the building in 2019.