When the Glasgow publisher Walter Blackie asked Charles Rennie Mackintosh to design a family home, the architect gave it a coat that was meant to protect it. The Hill House, built between 1902 and 1904 in Helensburgh on Scotland's rainy west coast, was finished in Portland cement render, a material then regarded as the modern answer to wind and rain. Traditional Scottish walls had been coated in lime instead.
The choice proved costly. Over the decades, the cement developed fine cracks through which rainwater seeped in. Lime is porous, so moisture that enters a lime-coated wall can evaporate out again; cement is not, and the water it let in stayed there. Repeated patching did little to help, and the walls eventually became saturated, threatening both the structure and the decoration inside.
The National Trust for Scotland, which has cared for the house since 1982, responded with an unusual shelter. In 2019, it completed a steel frame over the entire building and wrapped it in chainmail: some 32 million small metal rings, joined by hand. The mesh stops rain driven sideways by the wind, yet air passes through it freely. Raised walkways inside the frame let visitors look down on the house from above.
Inside the shelter, the walls were left to dry slowly, because walls that lose water too quickly can be damaged in the process. Once they had dried enough, workers began chipping the old render away, and specialists set about developing a replacement that would keep Mackintosh's appearance while allowing the walls to breathe.
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