Easy projects - easy language!
This section contains DIY woodworking and building projects or articles with simple, easy-to-follow instructions and explanations.
How to prepare the ground, pour and finish concrete
Example: A small shed floor: Part two
A step-by-step example of how to make a concrete slab floor for a 1800mm x 1800mm (6ft x 6ft) garden shed.
Instructions continued...
Safety Tip: Prolonged contact with fresh concrete will burn your skin. Wear safety goggles, gloves, rubber boots, and long sleeves when working with concrete.
Step 7. Picture above.
Start pouring the concrete into the pour area. Fill up the trench (footing) first to a height approximately 75mm (3") below the top of the formwork.
You can now place your rod of reinforcing steel on top of the concrete.
The reinforcing steel will help to control cracking and also help hold the concrete slab together.
|
|
Step 8. Picture above.
Lay a rod of #3 rebar (which is 10mm (3/8") thick reinforcing steel), around the perimeter of the pour area. The rod should be at least 50mm (2") in from the formwork and at least 50mm (2") down from the top of the formwork.
Wherever the reinforcing rod joins, make an overlap of at least 400mm (16") and tie together with tie wire.
For more information on reinforcing steel
click here.
|
Step 9. Picture above.
Fill the pour area up with concrete approximately to the height of the top of the formwork.
Tap around the outside of the formwork with a hammer. This will vibrate the wet concrete and help it to settle, as well as getting rid of any air pockets.
Use a straight piece of lumber (the bracing piece off the formwork will do) to "screed" or level out the concrete. Work the screed board back and forth with a sawing motion along the tops of the formwork until the concrete is level all over
|
|
Step 10. Picture above.
Smooth over the level concrete with a trowel or float. Hold the blade flat against the surface and sweep it back and forth in wide arcs.
Tip: you will probably not get it near perfect in the first going-over, but that doesn't matter. Leave it until it dries a bit or until all the excess surface water has evaporated and then re trowel.
A novice may need to go over it another two or three times to get a nice smooth finish, letting it dry a bit before each going over
|
|
Did you know? A concrete finishing trowel is made of steel. It is basically a rectangular piece of flat steel with a handle on it used to smooth over wet concrete. A wooden float is the same sort of thing but made of wood.
For concrete floors that are inside, a smooth finish is usually required and so a steel trowel should be used because it gives a smoother finish.
However, outside concrete slabs, paths etc could get slippery in the wet if the finish is too smooth, so a wooden float would be better
|
Step 11. Picture above.
Re trowel when all the excess surface water has evaporated. If the finish is still not as good as you would like, then let it dry a little bit more and then give it yet another going over with the trowel. Each time gets easier and makes the concrete more smoother.
|
|
Step 12. Picture above.
The formwork can be taken off the next day ONLY if it can be easily removed. If for some reason the formwork needs a lot of hammering and knocking to remove it, then best leave it in place for three days or so, until the concrete is hard enough to withstand the punishment.
|
NOTE: The concrete will now need to set (cure). Keep the concrete moist for about three days by hosing with a fine mist every now and then. This is especially crucial in warmer conditions.
Concrete in direct hot sun should be covered with some type of building wrap, roofing felt or shaded, for the curing period. If you must pour the concrete on a very hot day, then leave it till mid or late afternoon.
Concrete sets very fast on hot days in direct sunlight and can be hard if not impossible to work with. This is especially a concern when you're hand mixing, which requires a bit of time.
|
