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.
You can avoid many common driveway problems with careful planning.
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 New Zealand 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.
Discussion Prior to Work Commencing
- 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.
Areas of Contractors Work to Monitor
- 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 additional information download IB 80 - Residential Concrete Driveways and Paths and MS 19 - New Concrete Driveways: What To Expect.