With its cool grey lines and sculptural yet imposing presence, concrete’s unique beauty can add intrigue to the simplest of architectural forms. However, it’s a demanding material and achieving the requisite standard of finish takes skill, patience, and even a dash of luck, according to Sean McAneney. 

Sean, together with Adam Smith, has run Toki Construction since 2014. They specialise in building bespoke, architect-designed homes across Sydney, and, with a reputation for chasing complex projects that ‘defy the odds’, Sean says their 18-strong team particularly ‘enjoy the challenge of crafting complicated concrete structures’. 

Toki’s affinity for off-form concrete construction began when it won a tender to renovate and extend a Federation home on Sydney’s lower north shore a couple of years ago. While it had ‘good bones’, the interiors were poky and dated. The project’s architect, Steve Koolloos of MCK Architects, says the clients wanted more living space, an upgraded master suite and a better connection to the outdoors. MCK’s design solution was to reconfigure the layout of the existing home and add a new open plan kitchen/living/dining to the rear, which plays out as a single monolithic off-form concrete shell, abutting and echoing the form of the original home – pitched roof and all. 

Sean and Adam have worked on numerous high-end builds throughout their respective careers and were familiar with the intricacies involved in restoring heritage homes. They lavished the external brickwork and interiors with attention, restoring and sympathetically modernising elements to gently ease it into the twenty-first century. 

The second half of this project – bringing the vast concrete addition to life – presented the level of technical and logistical challenge that Toki Construction thrives on. At roughly 10 x 6 metres, with a 35-degree pitched roofline, it’s a formidable example of their skill and craftsmanship, their determination and unwillingness to compromise.

Construction began with ‘some reasonable groundworks and paring down to bedrock to support the structure,’ Sean says. ‘The polished concrete floor was a structural slab that was polished, as opposed to a topping slab. That posed a few challenges as we couldn’t just anchor our formwork down anywhere.’ The walls went up in a set sequence, with Basix requirements necessitating two pours for each: ‘You’ve got a wet wall and a dry wall, with insulation sandwiched in between to give it the correct thermal properties.’ 

Planning how to build a pitched roof in off-form concrete involved intensive research and some high-level problem-solving: not only was this a demanding task from a structural point of view, but because the concrete was to be left exposed through the interiors, a flawless finish was essential. 

‘There is 52 tonnes of concrete in that roof, and if you get it wrong it’s just so unforgiving, so we spent a lot of time trying to get comfortable with what we were trying to do. It’s not like there was a “good practice guide for pitched concrete roofs” to pick up and reference,’ Sean laughs. 

What they knew for sure was that the quality of the formwork was critical to achieving the requisite clarity of finish for the raked interior ceiling, and they put an extraordinary amount of care into its construction. Rather than sitting it on chairs (and risk leaving marks), the formwork was suspended. ‘All joints were well sealed so there’d be no bleeding of concrete, because that can leave an unfavourable effect,’ Sean says. 

Adding another layer of intricacy, the gridlines formed by the sheet joins in the finished ceiling had to align with other architectural elements in the interior space. ‘While that’s not difficult to achieve if you know what you’re doing and you care for the detail, it took 100 per cent planning and commitment from an early stage of the build. Although it’s structural, it’s also the finished element, and the gridlines needed to read true to other finishes, such as the joinery, door heights, mullions and window dimensions, which we didn’t even have onsite yet.’ 

To this end, ‘we were really clinical in our setout’, Sean says. ‘Every sheet of form ply was checked for square.’ Placement of coil ties, Z-bars and nails was carefully mapped out to follow the grid pattern. 

Sean asked the engineer if they could put a higher slump in the concrete (i.e. a wetter mix) to make it more workable. They poured a 1200mm wide strip on each side, alternating sides and covering the concrete to protect it from damage and the weather, until they reached the top. ‘We didn’t want to just load up too heavy on one side and put stresses on the walls.’

A nail-biting 28 days followed as the concrete cured to 32MPA. ‘That was an anxious wait…we were thinking, did we vibrate it enough, is it going to be boney, what’s it going to look like? Which made it all the more rewarding when we stripped it, and it just looked perfect.’

The finished room is resplendent in its simplicity. With glazing to the entire northern elevation and the double-height raked ceiling soaring above, the visual weight of the concrete is perfectly counterbalanced by the lightness and sheer volume of the space. Decorative finishes were kept to a minimum, bringing the precision of Toki’s work – the crisply rendered joints and lucidity of the concrete – into sharp focus.

The home, which Toki dubbed ‘Concrete Extruded House’, took around seven months to complete. The clients absolutely loved the finished result, and it also went on to attract several high-profile industry accolades, including the 2019 HIA NSW Renovation/Addition Project award. Even more satisfyingly, the project’s overall success launched Toki Construction into a higher echelon of work. 

‘It was a really cool experience,’ Sean says. ‘We had a great architect, great clients and a beautiful outcome. It’s got a special place for me because it was testing everything we knew at the time. It wasn’t a big budget build; it was all off the back of hard work and ensuring we got it right.’