Interlock sinks and shifts because of the base underneath, not the pavers. A thin or poorly compacted granular base, washed-out bedding sand, or a missing edge restraint lets blocks settle and spread, and Ontario freeze-thaw heaves a weak base every winter. A properly built interlock patio starts deep, compacted, and edged.
The base does the work, not the stone
People shop for pavers by colour and pattern. That is the part you see, and it is the part that almost never fails. The work happens below the surface, in the layers nobody looks at once the job is done.
A patio or walkway done right is built in order, from the ground up:
- Excavate to depth: we dig out the soft topsoil and dig down far enough to fit a real base, not just enough to drop a stone in.
- Compacted granular base: we bring in crushed granular, lay it in lifts, and compact each lift so it locks together and stops moving.
- Deeper where it has to be: the base goes deeper on clay, and deeper again for anything driveable. A driveway base is thicker than a patio base because it carries a car, not a chair.
- Edge restraint: a solid edge around the whole field so the outside rows cannot creep outward.
- Bedding and jointing sand: a thin setting layer the pavers sit on, then jointing sand swept into the seams to lock them side to side.
Skip or shortcut any one of those, and the patio is living on borrowed time. The good news is the reverse is also true: get the base right, and the surface stays flat for the long haul.
Why a weak base heaves and ruts in winter
This is the single biggest reason interlock fails in this part of Ontario. Our ground freezes and thaws over and over through the winter. When water sits in a thin or poorly compacted base and freezes, it expands and pushes the whole patio up. When it thaws, everything drops again. That cycle, repeated, is interlock heaving, and it shows up as a patio that is humped in the middle, lifted along one edge, or rutted where a base was never compacted properly.
For comparison, deck footings and foundations in this area bear on undisturbed soil below the frost line, roughly 1.2 m (4 ft) down, so frost cannot lift them. A patio does not go that deep, so it cannot rely on depth alone. It relies on a clean, well-drained, well-compacted granular base that does not hold water and does not settle. A base that is too shallow, full of soft soil, or never properly compacted will move with the frost every single year.
Why pavers shift and spread sideways
Heaving is up and down. Shifting is sideways, and it has its own causes. If you have ever wondered why pavers shift apart and open up gaps along the edges, it almost always comes back to two things.
- Bedding-sand washout: water running under the pavers carries the fine setting sand away. Once that sand is gone, the pavers have nothing to sit on and start to rock, tip, and dip.
- A missing or weak edge restraint: without a firm edge holding the field together, the outside rows slowly walk outward. The whole patio spreads, the joints open, and the pattern goes crooked.
Together those two problems explain most loose, gapping, wandering interlock. The pavers themselves are fine. They simply have nothing holding them in place.
Hamilton-area soil makes base prep matter more
The ground around here is not one thing, and that changes how deep we dig. Heavy clay is common on the Mountain and around Ancaster, and clay holds water and heaves hard, so it needs a deeper, better-drained base. Closer to the lake in north Stoney Creek and along the Burlington shore, the ground runs to sandier loam. Up near the escarpment edge in Dundas you can hit shallow soil over rock.
The fix is the same standard everywhere: dig to depth, build a compacted granular base, go deeper on clay and for anything that gets driven on, and move water away so it never sits under the stone. That is why two patios on two streets can need two different base depths. We size the base to the soil, not to a one-size number.
The paver settling fix: lift, correct, reset
Here is the honest part. You cannot fix a sunken interlock patio from the top. Adding more sand on top, re-leveling individual stones, or hosing fresh sand into the joints buys a season at most, because the problem is underneath. The real paver settling fix means going back to the base.
Done properly, the repair runs like this:
- Lift the pavers: we pull up the affected pavers and set them aside in order so the pattern goes back the way it was.
- Correct the base: we fix what failed. That can mean adding and compacting granular, rebuilding a base that was too thin, sorting out drainage so water stops pooling, and adding the edge restraint that was missing.
- Reset and lock it in: fresh bedding sand, the pavers back down level, a proper edge, and jointing sand swept into the seams.
It is more work than a quick top-up, but it is the only repair that lasts. Fix the base once and the surface stays put.
One thing to check before any base gets dug
An at-grade interlock patio or walkway generally needs no building permit. It is treated as landscaping, not a structure, as long as it sits on the ground and is not an elevated, deck-style platform. Grading, lot-coverage, and setback rules still apply, and the patio has to shed water away from the house and not onto a neighbour.
The one step that is not optional: locates. Before anyone digs the base, the buried utility lines have to be marked through Ontario One Call. It is free, and in Ontario it is the law, whether you are digging one post hole or excavating a full patio base. We book the locates before any machine touches the ground.
Frequently Asked Questions
Why does my interlock patio sink in one spot but not others?
A low spot almost always means the base under that area was thinner, softer, or never compacted as well as the rest. Water pools there, washes out the bedding sand, and the pavers drop. The fix is to lift that section, rebuild and compact the base, and reset the stones level.
Can you fix sunken or heaved interlock without replacing the pavers?
Usually, yes. The pavers themselves are rarely the problem, so we lift them, correct the base underneath, and reset the same stones. We only replace pavers that are cracked or chipped. Most of the original interlock goes right back down once the base is rebuilt properly.
How do I stop my pavers from shifting and spreading apart?
Shifting pavers come from a missing edge restraint and washed-out jointing sand. A firm edge around the whole field stops the outside rows from creeping, and properly compacted bedding plus fresh jointing sand locks the pavers together. If the base under them is also weak, that has to be corrected at the same time.
Get your interlock built or fixed on a base that holds
Whether you want a new patio or walkway that stays flat, or you need a sunken one rebuilt from the base up, The Hammer Construction does the digging, the base, and the resetting in-house. Licensed and insured. Get a free quote at our online estimator, call or text (647) 424-1148, or email hello@thehammer.construction