How to lay a concrete slab

The bulk of the work in laying a new slab for a shed, path or driveway is in the excavation and preparation of the formwork.
To level a sloping site or bring in roadbase and sand filling material, hire an excavator or a skid steer loader for the day from Kennards Hire.

Plan on taking a day to construct the formwork and one to lay the slab. If the slab is large, divide it in half with a length of formwork, completing a section at a time. This slab required 300mm high formwork for a perimeter edge beam.

TIP Driveways require formwork that’s 100mm high.

Step 1

Prepare the formwork
Set out a stringline to mark the slab and position the corner pegs. Cut a 290 x 45mm board as one side, securing to the pegs and checking with a spirit level. Position pairs of pegs and braces spaced every 600mm to hold the formwork.

Step 2

Set the corners square
Position a board for the width of the slab, securing to the formwork and pegs and setting out a diagonal stringline to check the corners are square. Secure pairs of pegs and braces along the board, repeating for the other sides.

Step 3

Compact the roadbase
Set a stringline and add roadbase to 150mm from the top of the slab base, measuring from the stringline. Slope the fill down along the edges for the beam, adding a 50mm layer of sand then screeding it level.

TIP The roadbase is about 75mm thick.


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