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

Quick Answer: Paving edge restraints prevent lateral spreading of flexible paving surfaces (block paving, resin bound, loose gravel). Without them, block paving edges crumble and the surface spreads within 2–3 seasons. The two main options are: concrete haunching (C20, 100mm wide × 75mm deep minimum, on the outer face of perimeter blocks) and flexible plastic/metal edge restraints hammered into the sub-base. Concrete haunching is more robust; flexible restraints are faster and better for curves.

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

Quick Reference Table

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Restraint Type Best Application Durability Installation Speed Vehicle Suitability
Concrete haunching All vehicle driveways Permanent Moderate (needs curing) Excellent
Precast concrete kerb (haunched) Formal driveway edges, adjacent to highway Permanent Slow (kerb setting + haunching) Excellent
Flexible plastic edge restraint Curved garden paths, straight pedestrian edges 10–15 years Fast Acceptable (not under vehicle tyres)
Steel/aluminium edge rail Straight or curved edges, driveways Long-lasting Fast Good
Brick soldier course Formal decorative driveways Permanent Moderate Good
Timber edging Garden paths, decorative beds only 5–15 years (treated) Fast Not suitable

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:

Where haunching may be omitted:

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:

Disadvantages:

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:

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:

Bedding and mortar:

Coursing options:

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