Laying a concrete slab
Step 1 - Prepare the site
Mark the work area using string wrapped tightly around pegs or stakes. (The work area should be 150mm wider than the finished area to allow a clear space to work in.)
Dig the area, marked by the string – this will be the work area. The depth of the work area should be:
- 100mm deep for concrete driveways or garage floors
- 75mm deep for paths and area without excessive traffic
- Allow an additional 75mm depth for a sub-base
Use a spirit level to ensure the area is flat.
NB. All topsoil should be removed from the work area. Build up with gap20 or rubble if required to desired level
Step 2 - Lay the sub-base
Dampen the work area base with water and then roll so that base is firm and compact.
Add a layer of small stones, gap20 or rubble to cover the work area base. Again dampen the stones with water and roll so that the base is firm and compact and no more than 75mm thick.
Step 3 - Erect the frame
The frame for the concrete slap needs to be constructed from timber which is 25mm thick and as wide and long as the desired concrete area, and should not allow for the working space (i.e. 150mm less than the pegged area).
Hold the timber frame in place with 50mm square stakes that are level with the timber frame when knocked in.
Check the level of the work area with a spirit level. Allow for any desired slope and check the diagonals.
Step 4 - Lay the concrete
Dampen the frame and the inside area of the frame with water.
Mix Cemix Multicrete (one 25kg bag will produce a slab equivalent to 400 x 400 x 75mm).
Empty the Cemix Multicrete into a wheelbarrow or mechanical mixer, or mix on a clean metal sheet or board. Add water gradually, mixing thoroughly until a smooth mix is achieved (under the ideal conditions a 25kg bag of Cemix Multicrete requires 2.5 litres of water). Use concrete immediately after mixing.
Start spreading concrete from one corner and make sure air is removed from concrete by tapping the concrete firmly – particularly in the corners. Spread the concrete evenly throughout the work area so that it is a few millimetres above the frame. Use a solid wooden board to thoroughly tap concrete down. Make the surface smooth by running the wooden board over the top of the wooden frame in a side to side motion so any excess concrete comes off the sides (screeding).
The surface of the concrete must remain damp for the first seven days - this can be done by lightly watering the area or spraying CEMIX Concrete CureWB on the freshly laid concrete slab . Leave the area for at least one week before use. After 28 days the concrete will achieve a minimum strength of 20 MPA.
NB: Control Joints on the concrete are required if the slab is more than 2m square.