Kerb Laying and Edging Installation in Dry Mix Concrete

Dry mix concrete, also called semi-dry or earth-moist concrete, is a mix of cement, aggregate and only a little water. It looks like damp sand. You can shovel it loosely, but it holds its shape when you squeeze it in your hand. Because it does not flow, it needs no formwork, and you can easily tap a kerb down into it to the right height.

Once compacted and dampened, the mix gradually hardens into a firm bed. For paths, patios, garden areas and ordinary driveways to a family house, this is fully adequate. For areas with heavy traffic or special constructions, a designer decides how the kerbs should be bedded, usually following the manufacturer's technical guidance and the relevant EN standards.

Setting out the line and level

The installer first stretches a string line between pegs or sets the height with a levelling instrument. The string marks both the top edge of the kerbs and their direction. At this stage the fall of the paved area matters too. Water should run away from the house, not towards it.

Digging and compacting the base

The trench is dug a little wider than the kerb so there is room for the haunch at the back. The depth depends on the height of the kerb and the load it will carry. Edging around flower beds needs a shallower trench, while a driveway edge needs to go deeper and often gets a compacted layer of hardcore or gravel. Topsoil and soft ground are removed from the bottom of the trench, and the base is compacted thoroughly.

Bedding, laying and haunching

Dry mix concrete is spread along the bottom, usually around 10 cm thick, and more where loads are higher. The kerb is placed, tapped down to the string line with a rubber mallet and checked with a spirit level. A narrow, even joint is left between units. Then a concrete haunch is formed on the outer side. This is a wedge of dry mix that reaches roughly a third to half of the kerb's height. Finally the concrete is dampened, and the kerbs are left unloaded for a few days.

• Garden edging: thin and light, used to separate lawns, beds and gravel areas where there is only foot traffic
• Path or park kerbs: somewhat sturdier, used for paths and patios where they have to hold the edge of the paving in place
• Road kerbs: thick and heavy, used along driveways and parking areas where wheels press against them
• Dropper or drop kerbs: with a chamfered or lowered edge, used at the entrance so a car can drive over smoothly

Concrete kerbs are the most durable choice and suit almost any situation. Plastic or metal edging works better in the garden as a lawn edge, but it will not reliably hold the edge of block paving. When choosing, ask yourself a simple question: will people only walk on this area, or will cars drive on it too? If cars will use it, choose a road kerb and a more substantial base. Also check that the kerbs are frost resistant. Winters with repeated freezing and thawing are hard on concrete in many regions.

The simplest case is a straight line on firm, level ground with good access. The job takes longer and becomes more demanding with:

• Curves and corners, where kerbs have to be cut or radius units used
• Slopes and large differences in level
• Soft, clay or waterlogged ground that has to be replaced or drained
• Heavy road kerbs that are awkward to carry by hand
• Removing old kerbs and taking away the rubble
• Tight spaces where neither a machine nor a wheelbarrow can get in

If you are building a driveway that connects to a public road or pavement, check first with your local council or highway authority. Lowering a kerb on the public side usually needs their permission and is often carried out by an approved contractor. Larger paved areas may also be covered by local building or drainage rules, so ask your local building authority rather than assuming no approval is needed. In a block of flats, any changes to the surroundings are agreed with the building management or owners' association.

In practice it often happens that kerbs look perfect once laid, and the problem only appears after the first winter. Typical causes are:

• A poorly compacted base, so the kerb sinks or tilts
• A missing or too low haunch, so the edge pushes out under pressure from the paving or a car
• A mix that is too wet, so it spreads when the kerb is tapped and the kerb "floats"
• Working in frost, or loading the kerbs before the concrete has hardened
• The wrong fall, so water collects along the kerb and washes out the bed

You can lay light garden edging around a flower bed or small path yourself. For road kerbs and driveways it makes more sense to call a firm that has proper compaction equipment.

1. Mark out the line with pegs and stretch a string at the height of the top edge of the edging.
2. Dig a trench a little wider than the edging and remove topsoil and roots.
3. Compact the bottom of the trench with a hand tamper or a plate compactor.
4. Mix the dry concrete so it holds its shape in your hand without water running out.
5. Spread the bed and level it roughly.
6. Place the first unit, tap it down to the string with a rubber mallet and check it with a spirit level.
7. Continue with the next units, keeping the same joint width and checking the line as you go.
8. Form a concrete wedge along the outer side and press it down firmly.
9. Dampen the concrete, keep it moist for a few days in warm weather and do not load it.
10. Only then backfill with soil or start laying the paving.

• The top edge of the kerbs matches the string line and nothing sticks up
• The line is straight or smoothly curved, with no steps
• The joints between units are even
• The kerb does not move or rock when you press it with your foot
• The haunch runs continuously along the whole length, and no bare concrete shows where there should be soil
• The kerbs have no chipped edges or cracks
• Water drains away after rain and does not stand along the edge