How to Install Edge Restraint (The Method That Stops Patios Spreading)

Why Edge Restraint Matters (Even If the Patio Looks “Fine” Today)

A patio isn’t a static object. It expands slightly in heat, contracts in cold, and the ground underneath moves by seasons. Without restraint, those tiny movements become a slow outward “creep”.

• Joints crack because the paving is spreading and the jointing becomes the “weak link”.
• Edges sink because the outside line loses support and starts to slump first.
• Slabs rock because once the perimeter moves, the bedding is no longer loaded evenly.

*(See also: Why Patio Joints Crack • Why Patio Slabs Rock)*

Edge Restraint Types (What Works — and What’s Mostly Cosmetic)

1) Concrete Haunch (Most Reliable for Domestic Patios)

A concrete haunch is a wedge of concrete that braces the outside of the sub-base and bedding layer. Done correctly, it stops lateral movement because it’s tied to the structural layers — not merely the slab edge.

• Pros: strong, long-lasting, suits most paving types, not fussy.
• Cons: needs correct groundwork; you can’t “cheat” the edge foundation.

2) Kerb Units / Block Edging on Concrete

A kerb or block edge can be excellent — but only if it’s set on a concrete bed with a concrete backing/haunch. Without that, the edge line becomes the first thing to drift.

• Pros: crisp finish, good visual boundary, can be very strong.
• Cons: if it’s only sat on mortar or soil, it fails early.

3) Metal/Plastic Edging Strips (Light Duty Only)

These can be fine for decorative gravel paths or very light use, but they do not provide structural restraint for a paving system. If your patio carries furniture, foot traffic, or large-format slabs, these shouldn’t be your “main restraint”.

*(Materials reference: Concrete Strength Grades)*

The Correct Installation Method (Concrete Haunch)

Step 1 — Build the edge foundation properly

The edge is where patios fail first because it’s easiest to under-dig and under-compact. Your sub-base must extend fully to the perimeter — not taper down to nothing.

• Dig to the same formation depth at the edge as the main field of the patio.
• Compact sub-base in layers (not dumped in one thick lift).
• Keep the edge line tight and straight — wandering edges create weak pockets.

*(Related: What Is a Patio Sub-Base? • How Thick Should a Patio Sub-Base Be?)*

Step 2 — Lay the bedding correctly (because restraint relies on it)

Edge restraint only works if the bedding is stable. If your bedding turns soft or weak, the edge can’t hold the system.

• Use a full bed (not dabs) for patios that are meant to last.
• Maintain proper thickness — too thin cracks; too thick slumps.

*(Deep dive: What Is a Bedding Layer? • Full Bed vs Dabs • Bedding Mortar Mix Guide)*

Step 3 — Form the concrete haunch

The haunch should brace the side of the bedding/sub-base and lock the perimeter in place. Think of it as a structural “shoulder” that stops sideways movement.

• Excavate a narrow trench along the outside of the patio edge (outside the slabs).
• Place concrete to form a wedge/haunch that contacts the side of the bedding/sub-base.
• Keep the top of the haunch below the finished surface so it doesn’t show.
• Let it cure properly — avoid disturbing the edge line while the concrete gains strength.

Step 4 — Finish the edge detail (so water doesn’t undermine it)

Even a strong edge fails if water is allowed to sit and soak the perimeter. The restraint is a structural detail — but water management determines how long it stays structural.

*(Related: Patio Drainage Basics • Why Patios Hold Water)*

Common Mistakes (Why “Edge Restraint” Often Doesn’t Restrain)

• Concrete placed against soil only: it doesn’t lock the paving system — it just hardens the ground beside it.
• Thin sub-base at the edge: the edge settles, then the joints open, then the centre follows.
• Haunch too small: it cracks or breaks away because it has no mass.
• Water ignored: saturated edges soften and wash out fines, undermining the restraint line.

If you’re seeing repeated joint failure, it’s rarely a “jointing product problem” — it’s movement. *(See: Why Patio Joints Crack)*

Can Edge Restraint Be Added Later?

Sometimes — but only if the edge foundation is still salvageable. Adding restraint to a collapsing edge is like bolting a fence to a wall that’s already leaning.

• If edges are sinking, you usually need to lift and rebuild the perimeter first.
• If slabs are rocking, the bedding likely needs correcting before restraint will help.
• If water is pooling, drainage needs fixing or the new restraint will be undermined again.

*(Related: Why Patios Sink at Edges • Why Patio Slabs Rock)*

Related Guides

• What Is Edge Restraint?
• Why Patios Sink at Edges
• Why Patio Joints Crack
• Concrete Strength Grades