The progress was made possible due to support from The National Lottery Heritage Fund, and can be viewed in a time-lapse video released by the conservation charity.

The entire roughcast removal is a significant step in the project to save The Hill House.

The Hill House was designed by Charles Rennie Mackintosh for publisher Walter Blackie and completed in 1904.

Having been in the care of the National Trust for Scotland since 1982, the house has become a globally recognised example of early 20th-century design. But it is also known as one of Scotland’s biggest challenges for building conservation. 

The original Portland cement roughcast, deemed innovative in its prime, trapped moisture within the building’s walls, which has caused extensive deterioration to the structure.

Finding the right way forward has necessitated years of research, testing and collaboration between conservation specialists, architects, engineers and craftspeople. 

The Hill House Box was completed in 2019 to safeguard The Hill House from the elements and allow the building fabric to begin drying out, while research was conducted to understand the condition of the house and determine the best way forward for conservation.

Supported by The National Lottery Heritage Fund, the project centres around The Hill House in Helensburgh and the Mackintosh Tearooms on Sauchiehall Street in Glasgow. 

After seven years protected by the Box, the Trust can now proceed with the next phase to make The Hill House watertight. 

Phil Long OBE, chief executive of the National Trust for Scotland, said: “The Hill House is one of Scotland’s most important architectural treasures, and the completion of the roughcast removal marks a significant moment in its conservation. 

“It follows years of careful research, monitoring and specialist work to better understand the building and determine how best to protect it for the future.

“Mackintosh Illuminated builds on this work, not only by securing the future of The Hill House, but by deepening the understanding of Charles Rennie Mackintosh and Margaret Macdonald Mackintosh and their remarkable contribution to art, architecture and design.”

Long added: “There is still a great deal of work ahead, and we will continue to need the support of our partners, funders and donors as the project progresses.  

“In recent months, we have all been reminded how precious and precarious Scotland’s built heritage is. The work at The Hill House demonstrates the complexity, expertise and commitment required to protect buildings of this significance.”