#HTE

Fixing an Architectural Experiment Gone Wrong

Experimentation in design is a tricky thing. Proponents of experimentation may argue it is required in order for designs to evolve. Critics may argue that experimentation is often wielded in the name of fashion rather than function.

Experimentation in architecture can be particularly perilous. More than a few architects referred to as “ahead of their time” have designed experimental structures later found to have significant problems. Frank Lloyd Wright famously ignored a structural engineering firm’s warnings about Fallingwater, which later required expensive repairs to reinforce the dramatic—and failing—cantilevered concrete balconies. Frank Gehry’s design of the organically-shaped Stata Center for MIT “resulted in pervasive leaks, cracks and drainage problems that have required costly repairs,” leading MIT to sue Gehry.

The latest famous architect whose widely-acclaimed design is now falling apart is Charles Rennie Mackintosh. Mackintosh’s design for Hill House in Helensburgh, Scotland, perhaps his most famous residential commission, is “dissolving like an aspirin in a glass of water.” The culprit is a poor choice of materials for the exterior cladding.

In the video at the bottom, Tom Scott will show you the effects and explain the solution. Before we get to that, I’ll explain the problem (Scott spends more time on the solution, and does an excellent job with it).

A traditional stone house finishing technique in Scotland is called harling. It’s a plastering process whereby the exterior of a stone house is coated in lime. While the lime is wet, small stones and pebbles are pressed into the surface. Once the mixture dries, the house now has a protective coating that still allows the building to breathe; lime is porous, and allows moisture to evaporate.

Rather than using lime, however, Mackintosh elected to harl Hill House using Portland cement. Whereas lime was at the time (1904) a tried-and-true material in use for centuries, Portland cement was relatively newfangled and offered a cost savings. Alas, applying it to Hill House “has led to maintenance problems ever since,” according to an essay called “Mackintosh and Materials,” by Ranald MacInnes, Head of Heritage Management, Historic Scotland. “We now know that cement is harmful to otherwise traditionally constructed buildings because it tends to craze, allowing water to penetrate but not to escape through natural evaporation.”

In 2017 the owner of the house, the National Trust for Scotland, reported the following grim news:

“Unfortunately for [original owners] the Blackies, who took up residence in 1904, and every owner of the house ever since, the Portland cement has never been a real match for the Scottish west coast weather. From the day the harling mix was applied, it has let in moisture.

"Now, after decades of driving wind and rain saturating the walls of the Hill House, the building’s long-term survival, including its unique interior finishes, is threatened. Over many years, solutions have been attempted by the property’s various owners but none has solved the problem. It now falls to the National Trust for Scotland to take radical steps to stop further deterioration and find the elusive answer.”

Those radical steps consist of building a gigantic “drying box” both to keep the rain off of the house and to let it dry out over a number of years.

Fascinatingly, chain mail has been chosen for the box’s walls; apparently they’re enough to stop sideways rain while still allowing air to pass through.

In Tom Scott’s video, you get a fantastic look at the structure, and thanks to the elevated walkways the NTS has installed, you can appreciate the house from angles previously impossible to attain: