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Residential Concrete Driveways
A well planned and constructed
driveway should last as long as your house does. This
page contains some basic tips on how to plan your driveway,
choose a contractor, and make sure they’re doing
a good job. Coloured or textured concrete surfaces are
not covered here.
Planning
You can avoid many
common driveway problems with careful planning.
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First, you need to consider the layout of
the driveway in relation to your section, giving thought to
where turning areas are needed, how the garage will be accessed,
and how the finished driveway will connect to the garden.
Next, draw an accurate plan of the section, showing where
you want your driveway to go.
Consider the slope of driveway. Assessing
where water falls, and where it drains, is crucial to avoid
puddling and flooding. Stepping into a pool of water as you
leave your car is bad enough, but water draining into your
house or garage is far more serious. The driveway surface
should be at least 25 mm above natural ground to allow for
self-drainage.
Your contractor will inform you as to where
the control joints should go – these are cuts made in
the concrete to allow for movement caused by temperature changes
and drying shrinkage. In other words, when concrete cracks
- you want to be able to control where it will crack and how
(e.g. in a straight line instead of randomly).
Concrete slab sections are best formed roughly
as squares. For rectangular slabs, the longer side should
be no more than 1½ times the shorter side. This rule
should ensure correct spacing of joints to minimise cracking.
Your contractor will be able to give you
planning advice to ensure your driveway complies with the
Building Code.
Choosing a contractor
- Ask for job references from any contractor you are
considering using
- Discuss with your contractor whether the existing soil
surface (subgrade) on which the driveway will be placed
is sound enough for the traffic load it will support,
or whether it will need improving.
- Ensure you receive a written quotation containing details
of everything that the contractor has allowed for, including
cutting of the control joints. Check whether they will
bring protective sheeting (if necessary) to protect your
house and garage from splashing during concrete placing.
- Ideally only one contractor should be involved in the
work (the main contractor). If sub-contractors are used
for any aspect of the job, this should be arranged by
your contractor, not by you. Having a main contractor
who is responsible for the whole job, will avoid arguments
between various parties if problems arise after the work
is completed.
Things to discuss
with your chosen contractor before they begin work
- Give the contractor your site plan. Your contractor
can note where the control joints should go and areas
that need to be protected from damage (e.g. gardens, trees
and letterboxes).
- Discuss the kind of surface finish that you want. You
might want to match the finish with that of other concrete
surfaces around your home, or create a surface you have
seen in a magazine or in a neighboring property.
- Remember that concrete is a variable material and can
‘set’ differently in different places and
under different conditions – even within the length
of the driveway itself.
Common Finishes
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| broom finishing (a bristle broom is drawn
across the surface giving it a lightly textured finish) |
wood floating (the surface is worked
using a wood float to give a lightly textured finish) |
steel floating (the surface is worked
with a steel float to create a very smooth surface which
may be slippery when wet |
What you should look
out for when the contractor is working
- Cool, overcast weather is ideal for pouring concrete.
It should not be poured if rain or frost is forecast.
Very hot days (especially if there is a lot of wind),
should also be avoided – if it is good weather for
drying the washing, it is not a good day to pour concrete.
- The area to be concreted should look smooth and firm
before the reinforcing steel is placed, with no soft or
muddy areas.
- The edge forms (‘boxing’) should be installed
to correspond with the agreed area marked on your plan
and should be securely fixed so that they don’t
move when the concrete is placed.
- Reinforcing steel should be spaced off the ground and
well secured against accidental movement.
- The contractor will spray the ground surface with water
just prior to the concrete being placed. This is to stop
moisture being drawn from the concrete mix into the ground,
which prevents the concrete from setting too fast.
- If pigments are being used, it is important that your
contractor uses plastic to protect your house, particularly
if it is clad with a textured coating as this is difficult
to clean if the pigment drifts onto it.
- Any drains or sumps need to be located and well supported
to prevent accidental damage.
- We recommend a minimum concrete strength of 20 MPa.
Ensure that the concrete delivered to site has no water
added to it by the concrete placers without the permission
of the supplier.
- Once the contractor has laid the concrete, they will
compact it with a vibrator or vibrating ‘screed’.
- The surface finish chosen should be applied when all
the water on the surface has evaporated. It is not good
practice to throw cement on to the surface when trowelling
it, or to add water to the surface to make the finishing
operation easier.
- When the driveway has been screeded, your contractor
may cover the surface with an anti-evaporative film, which
helps to control early setting and cracking.
- Control joints need to be cut within 24 hours of pouring
and within 12 hours if it is a hot day.
- Ensure your contractor applies a curing membrane to
the surface as soon as it can be walked on.
- Keep vehicles off the drive for at least 7 days. During
extended periods of cold weather extend this time by another
5 days.
For more information
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