Formwork to slab on ground

Summary

This instructional video demonstrates the process of creating formwork for a slab on ground with a step or rebate. It emphasizes the importance of this feature for brick veneer and timber frame construction, ensuring proper drainage and moisture protection. The video guides viewers through marking, transferring points, laying timber boards, and using different support methods like pegs and ledgers. It also covers the use of waffle pods for reduced concrete thickness, reinforcing with mesh, and the importance of allowing the slab to cure for seven days before removing formwork.

Takeaways

• 🏡 The video focuses on constructing a slab on ground with a step or rebate for a house, which allows for proper drainage and separation from the timber frame.
• 📏 The process begins with marking and setting out the slab area, utilizing string lines and transferring marks to the ground.
• 🚫 Formwork for slabs should not be cut to exact length to facilitate reuse; timbers are extended past the points.
• 📍 Edge boards are used to form the edges of the slab, supported by pegs or ledgers to maintain their position and straightness.
• 🔨 Pegs can be problematic if they hit rocks or hard ground, so ledgers are sometimes used for better support and adjustability.
• 🔩 Joining edge boards with cleats is necessary when a single board is not long enough to span the distance.
• 📏 Straightness of the formwork is checked using timber blocks and string lines to ensure even distribution of concrete.
• 🛠️ Alternative support methods include using brackets that screw onto the bottom edge board to support the top edge board.
• 🏗️ For non-heavy traffic areas, waffle pods (styrofoam) are used to reduce the thickness of the concrete slab, saving on materials.
• 🧵 Reinforcement is crucial; trench mesh is placed in the lower half of the slab, and fabric reinforcement or mesh is added on top of the waffle pods.
• ⏱️ After pouring the concrete, it's recommended to wait at least seven days before removing formwork to allow for initial curing, with full strength achieved in 28 days.

Q & A

What is the main feature of the slab on ground discussed in the video?

The main feature of the slab on ground is that it has a step or a rebate, which allows the brick veneer to go on the lower edge and the timber frame to sit on the top, facilitating the installation of flashing and weep holes for moisture drainage.

Why is it important to have a step or rebate in the slab?

A step or rebate in the slab is important because it allows for the separation of the brick veneer and timber frame, which helps prevent moisture from coming into contact with the timber frame, thus protecting it from potential damage.

What method does the video suggest for marking and setting out the slab on ground?

The video suggests using string lines from the marking out stage and transferring these marks onto the ground using spray paint, lime, or scratch marks to guide the placement of the formwork.

Why shouldn't formwork timbers be cut to exact length during construction?

Formwork timbers should not be cut to exact length to allow for reusability. Extending them past the points allows for adjustments and makes it easier to reuse the timbers in other projects.

What are the two methods shown in the video for supporting edge boards during formwork?

The two methods shown for supporting edge boards are using pegs directly driven into the ground and using a ledger with two pegs that can be slid into place without needing to be directly against the edge board.

How can you ensure that the edge boards are straight during formwork construction?

To ensure the edge boards are straight, the video suggests using a string line wrapped around blocks of the same thickness on either end of the board, with a block in the center to check for straightness. If the block fits snugly without a gap, the edge board is straight.

What is the purpose of the 150mm gap mentioned in the video when setting up the formwork?

The 150mm gap is to create the step or rebate in the slab. The top edge board is set back 150mm from the bottom edge board to form this step, which is necessary for the brick veneer and timber frame construction.

What alternative to timber edge boards can be used for formwork, as mentioned in the video?

As an alternative to timber edge boards, brackets can be used which simply sit over the bottom edge board and are screwed on, providing support for the second edge board.

Why are waffle pods or styrofoam pods used in the center of the slab?

Waffle pods or styrofoam pods are used to reduce the thickness of the concrete in areas that won't experience heavy loads, thus saving on material and cost while still providing adequate support for lighter loads like furniture and people.

What is the recommended waiting period before removing formwork after pouring the concrete slab?

The video recommends waiting approximately seven days before removing the formwork to allow the concrete to gain some strength, although it typically takes 28 days to reach its full designed strength.