Installing Kerbs and Edge Restraints: Getting the Foundations Right
Choosing the right kerbs and edge restraints is only half the job. To perform properly, they must also be installed correctly. Even the strongest kerb will fail to provide effective support if it is poorly founded, incorrectly aligned or inadequately restrained.
Kerbs, edgings, channels and restraints perform an important structural role within a pavement. They help prevent movement, contain bedding materials, support paving at vulnerable edges and, in some cases, contribute to drainage. Because of this, their installation should be treated as a critical stage of the construction process rather than a finishing detail added at the end of the project.
Start with a Solid Foundation
Every restraint requires adequate support beneath it.
The exact installation method will vary depending on the design and the type of restraint being used, but BS 7533 identifies three common approaches:
- Bedding onto hardened concrete using mortar.
- Installing directly onto fresh concrete.
- Fixing restraints to an existing surface using a suitable bonding system.
Whichever method is chosen, the key objective is the same: provide a stable and durable foundation that prevents movement throughout the life of the pavement.
In many domestic paving projects, a concrete foundation beam or race will provide the most practical solution.
Setting Out Before Installation
Accuracy at this stage is essential.
Kerbs and restraints often define both the finished edge of the pavement and the levels used for subsequent construction. Errors introduced now are likely to be reflected throughout the project.
Before installation begins:
- Confirm lines and levels.
- Check drainage falls.
- Verify finished heights.
- Confirm positions of drainage channels and fittings.
- Establish string lines for alignment.
Taking time to set out accurately makes the installation process considerably easier and helps avoid costly corrective work later.
Bedding Kerbs onto Concrete
Where kerbs are installed onto an existing concrete foundation, they are typically bedded on mortar.
The mortar bed provides a means of adjusting levels and ensuring full support beneath the unit. Mortar that has begun to harden should never be reworked or reused. Fresh mortar should be used throughout the installation process to achieve a reliable bond and consistent support.
Where joints exist within the concrete foundation beneath, corresponding joints should generally continue through the bedding layer and remain closely aligned with the joints between the kerb units above. This helps reduce the risk of future cracking and movement.
Installing Directly onto Fresh Concrete
An alternative approach is to install kerbs directly onto freshly placed concrete.
This method can be efficient but requires care during installation.
The concrete must be firm enough to provide support while still allowing adjustments to line and level. Units should be positioned carefully and pressed firmly into the concrete to achieve full contact and adequate support.
Where necessary, temporary support may be required to prevent fresh concrete from slumping before it hardens sufficiently. Concrete haunching should only be added once there is no risk of displacing the kerb from its correct position.
Understanding Jointing Requirements
Kerbs should not normally be installed tightly against one another.
Small gaps help accommodate minor movement and reduce the risk of edge damage during installation and in service. For most concrete and natural stone kerbs, joints are typically left slightly open rather than being tightly butted together.
Where wider joints cannot be avoided, an appropriate mortar joint may be required.
Clay kerb units generally require larger joints than concrete or stone products and should be installed in accordance with the manufacturer’s recommendations.
The objective is consistent joint widths that look professional and perform well over time.
Supporting the Kerb with Haunching
Once the restraint has been positioned correctly, it requires lateral support.
This is normally achieved using concrete haunching placed behind the kerb or edging.
Haunching serves several important purposes:
- Prevents the restraint from leaning.
- Resists traffic forces.
- Supports paving loads.
- Reduces movement caused by soil pressure.
- Increases long-term stability.
Effective haunching is particularly important on driveways, access routes and any area subjected to vehicle loading.
Installing Curves Correctly
Curved paving edges demand special attention.
Where small-radius curves are required, standard straight kerbs can create awkward joints and inconsistent alignment. For tighter curves, purpose-made radiused units or shorter kerbs usually provide a much better result.
Before permanently fixing curved kerbs:
- Dry lay units where possible.
- Check the visual alignment from multiple angles.
- Confirm joint consistency.
- Verify the smoothness of the curve.
A curve that appears acceptable from one position may reveal irregularities when viewed from another. Taking time to check alignment before fixing units in place usually improves the finished appearance significantly.
Cutting and Trimming Kerbs
Occasionally, kerbs need to be cut to suit site conditions, corners or curved alignments.
When trimming units:
- Avoid producing excessively short pieces.
- Maintain consistent joint widths.
- Position cut units carefully.
- Ensure cuts are clean and accurate.
Poorly positioned small cuts can detract from the overall appearance of a project and may also reduce durability.
Consider Drainage Details
Kerbs and restraints often interact with drainage systems.
For example:
- Channel units may collect and convey water.
- Combined kerb-drainage systems may be used.
- Dropped kerbs require careful level control.
- Drainage channels often form part of the edge restraint system.
Because of this, drainage requirements should always be considered when setting levels. Small errors can result in ponding, ineffective drainage or poor transitions between paving and drainage features.
Weather Matters
Like many aspects of paving construction, the installation of restraints is affected by temperature.
Concrete and mortar should generally be installed within suitable temperature ranges. Excessively hot weather can accelerate curing, while freezing conditions can compromise strength development and long-term performance.
Where conditions are unsuitable, it is often better to delay installation than risk problems developing later.
Good Paving Starts at the Edges
Kerbs and edge restraints form the framework that supports the pavement. If they are accurately set out, properly founded and securely supported, they provide the stability needed for the paving to perform as intended.
Many paving problems begin at poorly restrained edges. By paying careful attention to installation methods, alignment, drainage and support, landscapers can create a strong foundation for the rest of the project and significantly improve the long-term performance of the finished pavement.
