Planning and Site Preparation

The most important step in placing concrete is planning.
Always plan every step before any concrete is delivered.
Proper planning avoids delays, wastage, segregation and
problems which develop from these.
To eliminate problems of Delay, Segregation and Wastage,
see CHAPTER 7 Transporting and Placing Concrete
SAFETY Workers on the site should always wear protective
clothing, strong boots and, if required, helmets or eye protection.
Always avoid direct contact with cement and never kneel in or
touch the concrete mix directly.Wear gloves or use barrier creams.
Ensure that anyone using heavy equipment, such as screeds or
vibrators, has been properly trained.
The following steps should be taken before any concrete is placed.
MEASUREMENT Measure and stake out the area to
be concreted and consider how thick the slab must be.
The thickness will depend on the weight the concrete
must carry (ie driveway carries the weight of a car
and needs to be thicker than a garden path).
THE FINISHING LEVEL Once the thickness of concrete has been established, work out
where the concrete will finish. Concrete cannot finish too high against steps or the external
house wall and should not cover any part of weepholes in the wall. The finishing level
shows how much digging or excavation must be done. Pavements must grade away from
buildings and boundaries.
STEPS Steps must have even risers.
EXCAVATION The ground should be excavated as deep
as is required by the finishing levels. Any roots or grass
must be dug out until there is firm soil to place on. Always
dig the hole wider than needed to allow for the formwork.
Try to keep the edges and corners square.





SUBGRADE The soil a concrete pavement or
floor rests on is called the subgrade. If the soil is
soft or varies in softness, a layer of crushed rock
should be used. If there are only a few poor areas
these can be dug out, refilled and compacted. It is
important that the soil evenly supports the concrete.
Many later problems can be avoided by properly
preparing the subgrade.
FORMWORK Formwork gives concrete its shape,
Formwork must be properly braced so it is strong.
It should not flex or move.
See CHAPTER 18 Formwork




SERVICES Plumbing, heating or electrical
services often run through a slab. These must be
in place before any concrete is poured.
UNDERLAY AND SERVICES The underlay, or
vapour barrier, is a heavy plastic covering the
ground to minimise water vapour rising through the
hardened concrete. Always overlap the sheets a
minimum of 200 mm and do not tape them. Tape
the edges of underlay only around drainage pipes
or services which pass vertically through the
concrete slab.
Termite protection may be required around service
penetrations and round the perimeter of the slab.



REINFORCEMENT LOCATION Reinforcement can be used to increase the strength of
concrete and/or to help control cracking.
For house floors resting on the ground it is placed in the top 1/3 of slabs and in the bottom
of trenches and footings.
The reinforcement must be covered by a set amount of concrete which protects the steel
from rusting. This is called cover. The amount of cover depends on whether it is inside or
outside and is measured to the top or bottom of the outer surface.
Reinforcement should be securely held for slab on ground construction. It should overlap a
set distance or from one piece of reinforcing bar, or wire fabric, to another and at the
corners of a trench.
See CHAPTER 17 Reinforced Concrete
ACCESS Clear access must be provided to transport the concrete.
If concrete is to be delivered by trucks make sure they have unrestricted access to the site
in all weather conditions.
PLACEMENT Ensure all planning and site preparation takes into account how concrete
will be placed allowing room for trucks, ramps for wheelbarrows, space for a pump etc.
JOINTS The position, type and number of joints should be planned well before the
concrete is placed.
See CHAPTER 11 Joints in Concrete
WASTAGE Good planning and site preparation reduces wastage. Reducing wastage can
cut costs, since up to 15% of concrete can be lost this way.