Wednesday 13 May 2009

concrete slab floor 1800mm x 1800mm


A step-by-step example of how to make a concrete slab floor for a 1800mm x 1800mm (6ft x 6ft) garden shed.

The steps for this task are:
Making up the formwork (the frame that borders the concrete and stops it spreading).
Positioning the formwork on prepared level ground.
Fixing the formwork in place with pegs.
Digging a trench around the perimeter of the project.
Mixing and pouring the concrete and placing a piece of reinforcing steel rod.
Screeding and finishing the concrete.
Dismantling the formwork.

preparing to make a concrete slab

Materials you will need:
Approximately 12m of 100x25 or 100x50 for the formwork, brace and pegs.
Three 40kg bags of Portland cement.
0.2 cubic meters (7 cubic ft) sand.
0.3 cubic meters (11 cubic ft) gravel 20mm diameter and smaller.
Handful of 75mm nails.

Make up the formwork out of 100x20 or 100x50 lumber. The lumber should be straight but a low quality grade will do since it will eventually be discarded. The formwork is the frame that borders the concrete and stops it from spreading.

Cut two pieces of formwork lumber exactly 1800mm (6ft) long and cut another two pieces approximately 2400mm (8ft) long. Nail the four pieces together so that they make up a square with inside measurements of 1800mm x 1800mm (6ft x 6ft).

Ensure that the formwork frame is square. This can be done by making the diagonals equal length. Simply measure diagonally from corner to corner (see Step 1. picture) and then measure the other opposing two corners. The formwork frame is square when the distance between the opposing diagonals are equal.

When the formwork frame is square, nail a piece of lumber on top of the formwork frame from corner to corner, to make sure the formwork frame remains square until pegged in place.

The formwork is now ready to be picked up and carried into position, but first make sure that the ground has been prepared, that is, made level, with all vegetation and any soft ground removed.

Lay the formwork in place. Ensure that it is level and then secure it by hammering pointed 50x50 (2x2) or 50x25 (1x2) pegs at 900mm (3ft) intervals against the outside of the formwork.

Nail the pegs to the formwork but not all the way in, as the nail will need to be pulled out later.

Dig a trench around the perimeter of the floor area about 100mm (4") deep and about the width of the spade wide or about 200mm (8"). This is like a 'footing' to give the perimeter of the concrete floor more depth and strength, as that is the part of the floor that will be supporting the shed walls.

Saw off the tops of the pegs so that they are even with the top of the formwork. The area is now ready for concrete.

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