Wanted: Trigger-happy water-pistol owners willing to soak a Scottish national treasure created by Charles Rennie Mackintosh

The National Trust for Scotland is inviting people to come and squirt water at Hill House, one of Charles Rennie Mackintosh's greatest buildings, to check whether its new protective covering actually works.

If you own a water pistol and are free on Saturday, September 28, the National Trust for Scotland needs you — for the dousing of a lifetime. The charity is looking for volunteers to squirt water at a historic house designed by Charles Rennie Mackintosh to test whether its new chainmail covering works.

Considered Mackintosh’s ‘domestic masterpiece’, Hill House — which sits on a hillside in Helensburgh, Argyll, with views across the Clyde estuary — was designed and built between 1902 and 1904 for Glasgow book publisher Walter Blackie and his family.

Virtually every detail of the property, from the austere architecture to furniture and fittings, was devised by the Scottish architect and his wife, Margaret Macdonald — Mackintosh went as far as suggesting how to clip the trees outside.

Hill House has a reputation for being haunted but its biggest problem is of a rather more mundane nature — the materials used by Mackintosh to build it have turned out not to be watertight.

Exposed to Scotland’s inclement weather and inadequately protected by the external render, its walls became saturated over the years and the house suddenly faced the risk of ‘dissolving like a sugar cube’.

In a bid to save the building, The National Trust for Scotland then took the ground-breaking decision to protect it from the elements with a steel-frame structure covered in mesh made from 32.4 million chainmail rings.

Raised walkways let visitors to see the house from a different perspective, while shielding it and allowing it to dry out.

However, the National Trust for Scotland now needs to check whether the covering — called The Box — is as waterproof as it needs to be, so they have devised what they deem to be the world’s first ‘mass wet-weather test’.

‘We really need to test out the chainmail from all angles to see how it’s working,’ says the House’s visitor services supervisor, Emma Sweeney. ‘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. We’ll have our experts on hand to monitor the experiment and explain why the Box is needed.’

The test takes place at 2.30pm on Saturday, September 28 and, states the Trust, ‘anyone with a water pistol is welcome to join in’.

Entry to the grounds is free and no booking is required. Participants will receive a thank-you voucher allowing free family access to the Hill House and Box any time throughout September and October.