SUSTAINABLE BUILDING
Rammed earth dates back to the Great Wall of China
The results were extraordinary. “Lab tests showed our walls hit 70 Newtons, 10 times stronger than a standard concrete block. Even pull-out tests for roof brackets massively exceeded requirements.” The walls are strong, yes, but they are beautiful too. “We also imprinted the character of scaffold boards – saw marks, knots – into the walls, like details you’d see in a cathedral. Every section is unique.” Tonnes of tamping Among the challenges, one stands out. “One of the biggest challenges was making a rammed earth lintel. On the curved wall of the property we spanned nearly four metres over a doorway. With stainless steel reinforcement we managed it, and it may be the largest curved rammed earth lintel in Europe.” McHale’s project unfolded by hand, 209 tonnes of material tamped into place, millimetre by millimetre. “Old-school square tampers gave us accuracy: just 4.0 millimetres height variation across a 36.7 metre curve, and 5.0 millimetres across a 26 metre straight. With air compressors it would’ve been messier.” The changing seasons brought unexpected lessons. “We worked through winter, which actually helped us learn. In cold weather you wait until 11am so the clay isn’t frozen. In warmer months, under tin roofs and plastic sheeting, it became like a greenhouse, so we had to treat the walls like lime, cover them in hessian and water them to prevent cracking.” It’s slow, deliberate work, but satisfying. “It’s sustainable and fully recyclable,” McHale notes. “Without cement, you could smash it down in 100 years and rebuild with the same material. Parts of the Great Wall of China are rammed earth – it lasts.” For McHale, the project’s success hinged on having a strong, collaborative partnership between builder, client, and experts willing to share knowledge. “You need a client who trusts the process – you don’t see the result until the shuttering comes off months later. It means sleepless nights,” he admits. Support came from unexpected places. “The client found a professor from Bath University – he’s like the Jedi of rammed earth. He gave me his number and guided
Behind this innovation is McHale’s confident curiosity to learn new techniques through trial, error. “We had to solve details like how to fix doors and windows into mud walls,” says McHale. “After many cups of tea with the architect, window supplier, and building control, we used a recycled foam product wrapped in DPC, tied in with fishtails and mud. Structurally, it worked brilliantly.” The material itself became a design tool. “The clients wanted a pink finish, not grey. Hereford clay is naturally red, so I swapped out grey sand for red pit sand and a pinky aggregate. I tested eight different mixes until we landed on 45 per cent sand, 40 per cent aggregate, 15 per cent clay, plus 10 per cent white cement for strength.”
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THE
all about shuttering,” McHale says. “You’ve only got one shot – once the mud is in, you can’t change it. Our clients wanted curves, soft edges, and tactile walls. “Concrete shuttering would’ve left faceted, 50-pence-coin shapes on the curves, so I started researching. I found people using scaffold boards, which you can bend with relief cuts. Each 3.9 metre board needed 98 cuts to bend. We made 360 of them. That was months of prep before the five months of ramming.” EARTH u’ve n, ed e d you etre ade p
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Master Builder
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