To the undiscerning eye, the Logie schoolhouse looks as if it is nothing more than a small, dilapidated, brick-built cottage. But the single-room structure, built around 1830, is an A-listed building made from mud. And it’s currently undergoing a pound;500,000 restoration.

“We are stitching it back together,” says Stephen Copp, of the National Trust for Scotland, the organisation leading the project at Hillside, in Angus.

The school has a “brick skin” and interior walls, so it was only when a wall collapsed, following years of neglect, that its true colours were revealed. It is, he says, a “rare survivor” from the area’s earth-building past.

For some communities in Angus (Montrose, Brechin, Edzell), decent building stone was hard to come by, Becky Little, one of the builders working on the site, explains to the pupils at Rosemount Primary, just minutes away from Logie. So, until the 19th century, they used what was available on their doorstep: large deposits of clay.

It is a building material in use all over the globe. “One third of all the people in the world live in buildings made from some sort of soil,” she tells groups of P4-7 pupils.

There are mud houses everywhere, from the Yemen to Devon. Some, like the Logie school, are quaint cottages; others are more exotic, resembling giant pots, with intricate designs carved into the clay. There are a number of gasps of “wow”, as Ms Little flicks from one photograph to the next. But not everyone is convinced about the wisdom of building houses out of mud - especially in Scotland.

“You think it would melt when it rained,” says Blair, 8, and in P4.

Paige, who is in P5, is as sceptical: “You would not think it would hold up for long enough to be there for, like, a thousand years. Mud is soft.”

To survive in the UK, mud houses need a good hat and a good pair of boots, says Ms Little. “You put on a big thatched roof with an overhang to keep the rain off, and you build on top of blocks to keep its feet dry.”

Building a mud house, she concludes, is like building a huge coil pot. And when the pupils get some hands-on experience, building a bench in their playground, they begin to see this for themselves.

A mixture of sand, clay, straw and water is pummelled to get the right consistency. “This would have been done by beasts - horses and cattle - when they were building these houses here,” says Ms Little.

Today - in place of cattle - there are primary pupils wearing wellies. Pitch forks full of the mixture are then transferred to the site of the bench, a semi-circle which will later be planted with thyme to make it smell nice, and patted down, using the back of the fork. As the height of the bench grows, Ms Little recommends walking along it to gel the different layers together.

Mud is a “good building material and is perfectly repairable”, she explains, but a lack of faith in it has led to many buildings being demolished, which is why the Heritage Lottery Fund was prepared to fund the workshops.

“This is about raising awareness, so people know these buildings are around,” she says. “There are quite a lot in Angus, with bits hidden behind bricks or cement. If people find it, they panic and knock it down, but it’s not a bad thing.”

Mud buildings are environmentally friendly because they are made from natural materials, she argues, not to mention good for your health. “These buildings tend to be cosy and warm, with good atmospheric humidity. If, for instance, there’s a lot of moisture in the air, the walls will absorb it and when it’s dry they let it out.”

The restoration, funded by Communities Scotland, Historic Scotland and Angus council, is due to finish in August. It will be rented out as a one-bedroom house.