Paving Edging and Restraints: Concrete Haunching, Flexible Edge Restraints and Why Edges Matter for Longevity

Summary

Edge restraint is the unsung factor in paving longevity. A perfectly laid body of block paving will fail from the edges inward if the perimeter is not properly contained. Block paving is a flexible pavement — it has no structural cohesion of its own, deriving its load-spreading ability entirely from confinement and interlock. Remove the confinement and the surface gradually migrates outward under traffic loading.

The failure mode is familiar: edges of block paving starting to look ragged, blocks spreading apart, the first course sitting proud of or lower than the adjacent surface, gaps appearing. All of these trace back to inadequate or failed edge restraint. Fixing it after the fact is possible but expensive — the perimeter blocks must be lifted, the restraint reinstated, and the perimeter re-laid. Prevention at installation is far cheaper.

The choice of restraint type — concrete haunching, flexible restraint, precast kerb, or brick soldier — depends on the site geometry, the visual requirement, and the adjacent materials. Each has its place. Understanding when to use which is part of good paving specification.

Key Facts

• Flexible pavement principle — Block paving, gravel, and resin bound are flexible pavements; they require lateral confinement on all exposed edges to maintain their integrity
• Concrete haunching — C20 concrete (or stronger), placed on the outside face of the perimeter paving; minimum 100mm wide × 75mm deep; must be poured after edge blocks are set, before interior is vibrated
• Curing before vibration — Haunched concrete must cure minimum 24 hours before the vibrating plate compactor is run on the adjacent blocks; vibration on fresh concrete disrupts the haunch
• Flexible edge restraints — Proprietary plastic or steel edge strips hammered into the sub-base; faster to install; no curing time; available in straight and flexible (curved) versions; not as robust as concrete haunching under vehicle tyre pressure at the edge
• Precast concrete kerbs — BS EN 1340; standard product for formal driveway and road edges; various profiles (bullnose, splayed, square); haunched in C20 concrete on both sides; most robust option for edges subject to vehicle overrun
• Brick soldier course — Single course of engineering bricks (Class A or B) or facing bricks mortared to the sub-base on bedding mortar; attractive, permanent, integral to the design
• Timber edging — Not suitable for vehicle areas; acceptable for garden paths and decorative beds; rots over time (treat with preservative; use hardwood or pressure-treated softwood)
• No restraint = no edge blocks — On boundaries where the paving abuts a wall, existing kerb, step or retaining feature, no additional restraint is needed at that boundary; the structure provides the confinement
• Peg spacing — For flexible plastic restraints, pegs should be hammered at 300–400mm intervals to avoid the strip springing back on curves; on straights, 500mm intervals are adequate
• Profile above finished surface — Edge restraint should finish flush with or no more than 5mm below the finished block surface; exposed edge restraint above paving surface is a trip hazard

Quick Reference Table

Detailed Guidance

Concrete Haunching: The Definitive Method

Concrete haunching is the most robust and durable edge restraint for block paving driveways. When done correctly, it prevents lateral movement of the perimeter blocks permanently.

Procedure:

1. Lay and level the perimeter (edge) course — The edge blocks (soldier course or sapper course) are laid first, before any interior blocks. They are set to the correct finished level and alignment using a string line. The sub-base beneath the edge blocks provides the base.

2. Mix and place concrete — Use C20 ready-mix or site-mixed concrete (1:2:4 mix). Place on the outside face of the edge blocks only — do not allow concrete to spill onto the block faces or the future interior of the paving. The haunch should be 100mm wide and 75mm deep, sloping from the top of the block edge down to the sub-base. Some installers bring the haunch to a point at the top of the block to shed water.

3. Protect from rain — Fresh concrete must be protected from heavy rain for 24 hours. Light rain is acceptable; heavy rain will wash out the cement paste.

4. Cure before vibrating — Allow minimum 24 hours at ambient temperature above 5°C before running the vibrating plate compactor over the adjacent blocks. In cold weather, allow 48–72 hours. Vibrating adjacent to uncured concrete can shear or crack the haunch.

5. Backfill later — Any topsoil or turf reinstated against the outside face of the haunch is done after the haunch has cured.

Where haunching is critical:

• All vehicle-accessible edges
• The bottom (road end) of sloping driveways, where vehicle loading creates the most lateral force
• Any edge where there is no adjacent structure to provide lateral support

Where haunching may be omitted:

• Edges abutting existing walls, permanent structures, or adopted kerbs/road surface
• Purely pedestrian areas where vehicle access is positively prevented

Precast Concrete Kerbs

Kerbs (BS EN 1340) provide both edge restraint and a finished edge profile. Common types:

Bullnose kerb — rounded top edge; the standard residential driveway kerb; available in 50mm × 150mm × 900mm and 50mm × 200mm × 900mm standard profiles.

Dropped kerb — lower profile for vehicle crossing; used at entrances; typically 40mm × 50mm × 900mm (see dropped kerb application for the highways approval process for public footway crossings).

Edging kerb (no. 50 or flush edging) — small profile for use as paving edging within a property; 50mm × 150mm; lower and less obtrusive than road kerbs.

Installation:

1. Set out the kerb line with a string line and level pegs
2. Bed each kerb on a 50–75mm lean mortar bed (1:6 or lean-mix concrete)
3. Haunch each kerb with C20 concrete: front and back faces; minimum 100mm wide on each side; the back haunching acts as the restraint for the paving
4. Point joints between kerb sections with 3:1 mortar (flush pointing)
5. Allow 24–48 hours to cure before laying paving

Flexible Plastic Edge Restraints

Flexible edge restraints (e.g. EcoEdge, Brickset, Coppice Edging) are extruded plastic strips with integral peg channels. They are hammered into the sub-base using a mallet and steel pin.

Advantages:

• Fast installation (no concrete mixing or curing)
• Flexible — can follow curves without cutting
• Invisible in the finished surface (installed flush with block top)
• Recyclable materials

Disadvantages:

• Less durable than concrete haunching under vehicle tyre pressure at the edge
• Can be dislodged by ground movement or frost heave on shallow sub-bases
• Pegs can pull out if the sub-base is not compact enough

Best application: Pedestrian areas, garden edges, paths, light-use driveways (regular family car). Not recommended as the primary restraint at the front edge of a heavily used vehicle driveway.

Installation tips:

• Stake at 300mm centres on curves; 500mm on straights
• Stake below the depth where frost heave can affect them (below the frost line, typically >150mm)
• Where a vehicle tyre could contact the edge strip directly (e.g. at a driveway entrance corner), supplement with haunching

Brick Soldier Course Edging

A single course of bricks mortared to the sub-base provides an aesthetically integrated edge that matches traditional or heritage properties.

Brick selection:

• Engineering bricks (Class A: water absorption <4.5%, compressive strength ≥125N/mm²; Class B: water absorption <7%, ≥75N/mm²) for high durability and frost resistance
• Facing bricks — acceptable for decorative driveways; choose a stock with F2 (frost resistance) rating

Bedding and mortar:

• Bed bricks on 50mm of C20 lean mortar or strong mortar (3:1 sand:cement)
• Point joints between bricks with 3:1 mortar
• Haunch with C20 concrete on the outside face

Coursing options:

• Soldier — bricks stood on end, long face visible; gives height but uses more bricks
• Sapper — bricks laid on their side, short face visible; lower profile; more stable base

Why Edges Matter: The Physics

Block paving relies on three mechanisms for structural integrity:

1. Vertical load spreading — load from vehicle tyre distributed laterally through the block layer and into the sub-base
2. Horizontal interlock — adjacent blocks prevent lateral movement of any single block
3. Edge confinement — the perimeter blocks are laterally confined so the horizontal interlock in the whole surface is maintained

If the edge confinement fails, the outermost row of blocks moves outward. The interlock with the next row in is then partially broken. That row moves outward slightly. And so on — the failure propagates inward from the edge. A driveway with perfect sub-base and perfect blocks will eventually fail if the edge is unrestrained.

This is why edge restraint must be installed before any interior blocks are laid and compacted — compacting without the restraint in place applies the very forces that will migrate the perimeter outward.

Frequently Asked Questions

The client wants grass right up to the edge of the block paving — can I use a plastic edge restraint?

Yes, this is the most common use of flexible plastic restraints — they allow turf to abut the paving level without a visible kerb. Install the strip at or just below the block surface level. Note: for vehicle driveway edges, supplement with haunching if the driveway will be used by anything heavier than a standard car.

How wide should the haunching be?

Minimum 100mm (4 inches) on the outside face of the edge block. If the adjacent material is soil or turf (which provides no lateral support), widen to 150mm. The concrete haunch doesn't need to be thick — 75mm depth is adequate. What matters is width and coverage of the full block height.

Can I use rapid-setting concrete for haunching to reduce curing time?

Yes — rapid-setting concrete (e.g. Postcrete or similar) cures sufficiently to resist vibration loading within 2–4 hours. This is useful in situations where you need to continue work the same day. Check the product's compressive strength — it should be at least equivalent to C20.

My existing block paving has no haunching and the edges are crumbling — can it be retrofitted?

Yes, but it requires lifting the perimeter blocks back 1–2 rows, excavating the sub-base edge, placing concrete haunching on the outer face, curing, then re-laying the lifted blocks. The cosmetic result depends on the condition and availability of matching blocks.

Regulations & Standards

• BS 7533-3:2005 — Code of practice for laying concrete block paving; includes edge restraint requirements

• BS EN 1340 — Concrete kerb units; requirements and test methods; relevant for precast kerb specification

• BS EN 771-1 — Specification for masonry units — clay masonry units; frost resistance classifications for bricks used in external paving edge

• BS EN 771-3 — Aggregate concrete masonry units; relevant for concrete engineering and facing bricks

• Interpave: Block Paving Design and Specification — edge restraint guidance in paving design

• EcoEdge: Flexible plastic edge restraint — product-specific guidance on plastic restraint installation

• block paving installation — full block paving installation methodology including the sub-base sequence

• block paving lifting repair — repair methodology when edge failure has caused surface spreading

• natural stone paving — edge restraint requirements for mortar-bedded natural stone

• driveway gradient requirements — how falls and drainage direction relate to edge placement