Precast the blocks and stack 'em up

Process used to build about 70% of a typical HDB flat looks simple, but it involves lots of measurements and planning

A tower crane lifting a precast facade wall into place on the 15th floor of the Hougang Crimson HDB project. The precast flooring is first put in place, followed by the facade walls and then the internal walls. The precast construction method boasts faster speeds among its advantages. Flats are built at an average speed of about two storeys per month using this method.

Desmond Lim, Desmond Lim, Photojournalist

The scene at the Sunway Concrete precast plant in Tampines appears to be a chaotic, dusty tangle of steel and concrete.

The Sunway Concrete Products precast concrete plant in Tampines. This plant is one of the company’s 16 plants in Singapore, Malaysia and Indonesia supplying precast components for HDB projects in Singapore.

But to an industry insider, the wheels of a well-oiled system are in place, with workers churning out tonnes of precast building components destined for construction sites islandwide.

The edges of a wall being smoothened after it is demoulded, to ensure that precast pieces fit well together.

According to the Housing Board, 16,900 Build-To-Order (BTO) flat units will be offered this year.

A worker tightening a brace bolted to a facade that had just been lifted into position in a Hougang Crimson block. The brace stays on until the adjoining walls and beams are put in place.

This number is on top of the 22,455 units launched last year.

A worker sorting out reinforcing steel bars, known as “rebars”. In the background are HDB facades that are waiting to be delivered to the worksite.

To cope with demand, the Housing Board (HDB) has been using precast components to build flats since the 1980s.

Precasting involves pouring cement into steel moulds to form various concrete components like facades, columns, staircases, household shelters and water tanks.

Workers’ safety helmets hanging outside the canteen in the Sunway Concrete precast plant in Tampines. An army of workers work almost daily to churn out tonnes of precast building components for construction sites islandwide.

About 70 per cent of a typical HDB flat is built using precast components which are supplied by some 16 plants in Singapore, Malaysia and Indonesia.

A hopper containing cement (top right of photo) is used to fill up a mould which will be left to set overnight. After the cement is poured in, a worker inserts a vibrator (right) into the mixture to make sure it settles evenly and to remove any air pockets which might affect the end product. The moulds are usually filled in the evening and left to set in the night.

This Lego-esque way of building is said to improve speed, efficiency and safety - it takes just a month to build two storeys.

Workers enjoying a movie projected on a makeshift screen inside the multistorey carpark at the Hougang Crimson worksite. Workers finished work early on this day to celebrate the “topping up” of the carpark – a stage of construction when the last structural precast component is installed. The company holds milestone celebrations like this to boost morale and reward workers.

However, the building process entails more than merely stacking up massive concrete blocks, some weighing up to eight tonnes.

"It looks simple but it is not.

"A lot of measurements and planning are done before the components are hoisted into place," says Mr Toh Chee Boon, project director with China Construction, who is managing the Hougang Crimson BTO project.

Wind direction has to be considered when tower cranes are hoisting the blocks.

A surveyor also has to confirm the exact location where the precast components are going to be installed based on architectural drawings, to prevent any misalignments.

Because of the complexity involved in building a block of flats, China Construction sometimes holds milestone celebrations, involving food and lucky draws for workers, after a building's last structural precast component has been installed.

It is an effort to reward workers and keep morale high, says Mr Toh.

He adds: "A happy worker will do a better job and I think we should appreciate them.

"After all, they left their homes to build ours."

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