Water pistol owners are being invited to drench a Charles Rennie Mackintosh masterpiece to see if a protective covering is doing its job.
The National Trust for Scotland installed the world’s biggest chainmail mesh around the Hill House to stop it dissolving “like a sugar cube”.
The property in Helensburgh, Argyll, is considered to be the architect’s finest domestic project.
But due to its design and materials it has soaked up water “like a sponge”.
Now the trust is inviting the public to bring water pistols to the property to test the 32.4 million chainmail rings in an experiment believed to be the first of its kind.
Emma Sweeney, visitor services supervisor at the house, said: “We’ve had some pretty wet days since the box went up but we really need to test out the chainmail from all angles to see how it’s working.
“We came up with the idea of the water pistol wet weather test as it’s something that everyone can get involved in and it should show how well the chainmail is doing its job.
“Anyone with a water pistol – the bigger the better – is invited to come down and Douse the House and we’ll have National Trust for Scotland experts on hand to monitor the experiment and explain why the box is needed.”
Battered by around 190 days of rain a year, the long-term survival of the building is in doubt and conservationists believe there is a danger its “priceless” interior could be lost forever.
The Hill House Box is the trust’s attempt to solve the problem of water damage at the property and to permanently save it.
It is a vast semi-transparent shelter around the main house – granted official museum status in June – consisting of a 165-tonne steel frame swathed in chainmail made up of rings weighing 8.3 tonnes.
The free Douse the House experiment takes place at 14:30 on Saturday 28 September.