Finished concrete slab for Unit 2
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Pouring Unit 2 slab

The end of 2018 saw a flurry of activity.  David and his crew finished Unit 1 so, in late-November, we moved out of our rental and into a beautiful, comfortable sustainable home.  However, the team weren’t resting on their laurels, despite Christmas fast approaching. They immediately started on preparations for the Unit 2 slab (aka Unit 2 thermal mass).

Clearing the site for the slab.

Two things stood in the way of starting Unit 2 foundations (literally).

Pulling down the carport to make way for the slab

After removing the solar panels on the roof, down came the carport.   The structure only needed the tiniest amount of encouragement to collapse in a heap.

Removing the garage was a bigger operation.  Before starting, the crew relocated the reclaimed floorboards and messmate timber we’d stored inside for a couple of years.  Layer by layer, they manhandled the timber down to the back of the property to create a new stack. Once the garage was emptied, it was dismantled, loaded onto a trailer and carted away to be rebuilt on another property.  I’m pleased about the old garage getting another lease of life.

Site cleared and ready for slab preparations

Clearing the site gave the green light to serious earthworks so the big yellow excavator burst into life. It was parked in the backyard like a giant garden ornament, just waiting for the right moment to get moving.

Excavator levelling the site for Unit 2

A sloping block means cutting into the ground on the south side, while building up the level on the north side.  The site needed a couple of days of cutting, filling and compacting to be ready for the next step in the process.

Site levelled and ready for the next stage of slab construction

Preparation for pouring a stiffened raft slab.

All that time and effort in  levelling the site is only a precursor for the real work of creating the slab.

To ensure a stable slab, the design includes bored piers.

Bored piers help support the concrete slab
Bored pier support diagram from Foundation Performance Association

Pockmarks appeared in the previously smooth surface. These are holes for the concrete piers.

Holes drilled for bored piers

Plumbers are next on the scene.  They dig trenches for laying a variety of pipes and then refill.  I wondered why they went to the effort of putting the earth back but the next activity answered my question.

The fun really begins with excavating trenches for beams under the slab. These trenches are laid out with geometric precision so the more random cuts made by the plumbers have to be refilled.  Beams are there to stiffen the concrete slab. Hence, Unit 2 is built upon a delightfully named stiffened raft slab.

Stiffened raft slab diagram
Stiffened raft slab (RMIT diagram)

During the next few days, the team adds all the bits and pieces shown on this diagram.

Adding precise amounts of bedding sand produces the desired floor level. How do I know this was done precisely? A laser level checked every section.

Bedding sand added to ensure correct floor level.

As soon as the level is correct, the sand is covered by insulation panels and a vapour barrier of black plastic covers the lot. Layers of steel mesh go into the trenches and onto the benches to reinforce the slab.  The finishing touch is wooden formwork to contain the concrete.

Preparations completed for pouring the slab

I could see the care and attention the team put into getting the foundations “just so”.  Now, all that’s missing is the concrete.

Slab poured in one busy day.

Careful scrutiny of the weather forecasts helped to choose a Goldilocks Day for pouring the slab – not too hot and not too cold.  No rain helped as well. With everyone in position, it was on for young and old.

A steady stream of VicMix trucks arrived and carefully backed down the driveway.  Just like Unit 1, the trucks delivered a special blend of concrete with a smaller carbon footprint than the standard mix.

VicMix truck delivering a load of concrete

Bravo Pumping transferred the concrete to where all the action happened.

Bravo Pumping transferred the concrete from truck to site

Most of the team busily poured and spread the concrete into the slab.

Team busy spreading concrete on the slab

After the last truck departed, the team ironed out any wrinkles in the surface.

Ironing out the remaining wrinkles in the slab

By the end of a busy day, everyone looked tired but happy about finishing the slab.  Another item crossed off the the construction to-do list.

Time to start on the Unit 2 frame.

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