What the restraint is actually resisting
An interlocking paver surface works because each unit is wedged between its neighbours and cannot rotate or slide. That interlock only exists if the field is in compression. Every time a load crosses the paving it pushes sideways as well as down, and that push has to end somewhere. In the middle of the field it ends against the next paver. At the edge it ends against the restraint, or it ends by moving a paver outward.
Once one edge paver moves, the joint behind it opens, sand washes out of the open joint, the next paver loses its wedge, and the failure walks inward. This is why paver patios almost never fail in the middle. It is also why the restraint is not a trim detail you add at the end if there is money left.
Only the open edge needs restraint, and people over-buy here
An edge that butts a house foundation, an existing concrete slab, a kerb or a proper retaining wall is already restrained by that thing. You do not run plastic edging along a wall. On a typical rectangular patio against a house, one full side is already held, which is a quarter of the perimeter you are not buying.
Be honest about what counts. A landscape timber pinned into soil with a few rebar stakes is not restraint; it is a long paver that will move along with everything else. A row of bricks set in mortar on undisturbed ground is closer, but only if it is bedded below frost depth in a climate that freezes. If you are unsure whether an edge is holding, treat it as open and restrain it.
Spike spacing, and why the curve is different
On a straight run the restraint is in tension along its length and the spikes mostly stop it sliding outward. Twelve inch centres is a common figure for straight runs on a well compacted base, but the number that governs is the one on the product instruction, because rigid and flexible restraint from different makers are not equivalent.
On a curve, the restraint has been bent against its own stiffness and is permanently trying to straighten out. Every spike is carrying that spring load as well as the load from the paving. Tighten the spacing to roughly half the straight-run figure through the curve, and tighter again on a small radius. A curve spiked at straight-run centres tends to look fine on installation day and to have visibly bowed by the end of the first hot summer, because the plastic softens and the stored spring wins.
| Condition | What to check |
|---|---|
| Straight run, compacted base | Manufacturer spacing, spike into base not soil |
| Curve | Roughly half the straight spacing, tighter on small radii |
| Ends and piece joints | An extra spike either side so the joint cannot hinge |
| Vehicle traffic | Heavier restraint, closer spikes, and a base built for the load |
| Base stops at the paver edge | Stop and fix it before spiking anything |
Topping up joints that have dropped
The sand calculation on this page is deliberately a top-up figure, not a first fill. On a new patio the joints are filled through the full thickness of the paver and that quantity belongs with the rest of the new-build materials on the paver patio calculator. On an existing patio the joints have usually lost the top half inch or so to rain, sweeping and a pressure washer used too close, and you are refilling only that.
The quantity is far more sensitive to joint width than people expect, because the joint area is a share of the whole surface and that share roughly doubles when the joint doubles. Measure several joints in different parts of the patio rather than assuming the nominal figure, and measure how far down the sand has actually gone by pushing a screwdriver into a few joints. Two joints an eighth of an inch apart in width will change the bag count noticeably.
The part a page cannot check
Restraint and sand are the visible edge of a system whose important half is buried. Base depth and compaction decide whether the patio stays flat, and both depend on the soil, on how the ground drains, and on what will cross the surface. Foot traffic and vehicle traffic are not the same specification and the gap between them is large. Compaction has to happen in thin lifts, and a base compacted in one thick pour is loose at the bottom whatever the plate compactor did on top. If the base is wrong, no amount of edging saves it, and the repair is a rebuild from the subgrade up.
Restraint also has to sit on base that extends past the paving, typically by a margin on each side, or the spikes are anchored in nothing. If you are setting the restraint on an existing patio and find soil under it rather than compacted stone, that is the finding, and it explains the movement you came to fix.
Questions people ask
Do I need edge restraint if the patio is surrounded by lawn?
Yes, and that is the case where it matters most. Lawn offers no lateral support at all, and the soil at the edge is the softest, wettest soil on the site because it is where surface water ends up. Grass growing against an unrestrained edge also lets roots work into the joints. The visible symptom is a wavy outer row and joints that will not stay full no matter how often you sand them.
Can I use concrete instead of plastic edging?
A concrete toe or haunch poured against the edge of the paving is a legitimate restraint and is common under vehicle loads, but it is a different job with different failure modes. It has to be poured on the base rather than on soil, it has to stay below the finished surface so it does not show, and in freezing climates it can be heaved by frost in ways flexible restraint is not. Plenty of installers use it. It is not the easier option, and it is not something to improvise mid-project.
How much extra restraint should I buy?
The five percent default covers offcuts at corners and the short piece at the end of each run. If the perimeter is mostly curves, or has several corners in a short distance, push it higher, because you will cut and discard more at each direction change. Buying one extra piece is cheap insurance, and unlike pavers, restraint does not have a batch colour to match.
Should I sand the joints before or after compacting the surface?
The usual sequence is to sweep sand into the joints, run the plate compactor over the paving with a protective mat, then sweep and fill again, because compaction settles the sand and drops the level. Expect to repeat that at least once. If you are using a polymeric product, follow the wetting and curing instruction on that particular bag exactly, including the weather window, since setting it in the wrong conditions is the common way people end up with hazed pavers or joints that never harden.
The patio has moved at one corner. Is more edging the fix?
Not on its own. Movement at a corner usually means the base under that corner has settled, washed out, or was never compacted, and adding restraint to a moving base just relocates the problem. Lift a few pavers at the corner and look at what is under them. If the bedding sand is thick, or the base is thin, or you find soil, that is the cause. Where the corner is also the low point of the patio, look at the fall across the surface too, using the hardscape slope calculator, because water arriving at that corner and sitting there is a likely reason the base gave up.