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How to prepare the ground, pour and finish concrete
Example: A small shed floor: Part one
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.
Materials you will need:
Approximately 12m (40ft) of 100x25 (1x4) or 100x50 (2x4) for the formwork, brace and pegs.
Three 40kg (94lb) bags of Portland cement.
0.2 cubic meters (7 cubic ft) sand.
0.3 cubic meters (11 cubic ft) gravel 20mm (3/4") diameter and smaller.
10 meters (30 ft) #3 rebar (which is steel rod that is 10mm (3/8") thick).
Handful of 75mm (3") nails.
Did you know? Cement is sold in bags of varying weights throughout the world. Common bag weights are: USA 94lb; Canada 87.5lb; UK 112lb; Australasia and parts of Europe 50kg and 40kg. There are also smaller bags sold as well.
Tools you will need: spade or small shovel; concrete finishing trowel; hammer; level; measuring tape; pencil; carpenters square; wheelbarrow; bucket.
Step 1. Picture above.
Make up the formwork out of 100x20 (1x4) or 100x50 (2x4) 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.
Tip: the formwork in this example DOES NOT have to be made up in place. It can be made up anywhere on even ground and carried in place later.
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).
Step 2. Picture above.
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.
Step 3. Picture above.
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.
Step 4. Picture above.
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.
Step 5. Picture above.
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.
Step 6. Picture above.
Lightly hose (dampen) the pour area with water prior to pouring the concrete. Work as quickly as possible when placing concrete in formwork. For instructions on how to mix concrete