Why Interlock Sinks: Base Depth, Frost Heave and Doing It Right
If you've seen a walkway with a dip near the door, a patio with a low spot that holds water, or a driveway with ruts where the tires go, you've seen interlock that wasn't built on a proper base. The pavers themselves are rarely the problem. What's underneath them is.
Here's why interlock sinks in Ontario, and how it's built to stay flat for decades.
Ontario winters are hard on hardscape
Every winter, water in the soil freezes and expands, then thaws and contracts. This freeze-thaw cycle pushes and pulls on anything sitting on top of it. If the ground under your interlock holds water, or if there isn't enough compacted base to spread the load, the surface moves.
That's frost heave, and it's the main reason poorly built interlock fails here.
The four most common causes of sinking
1. Not enough excavation
For a walkway or patio, we excavate 10 to 12 inches depending on soil conditions. For driveways and extensions, 16 to 18 inches. Some installers dig 4 to 6 inches to save time and money. That leaves soft topsoil too close to the surface, and it settles.
2. Poor compaction
Granular base needs to be laid and compacted in thin layers, called lifts, with a plate compactor. Dumping all the gravel in at once and compacting the top leaves loose material below that settles later.
3. Water with nowhere to go
If the surface isn't sloped away from the house, or downspouts empty onto the pavers, water sits in the base. Wet base is weak base, especially in freeze-thaw season.
4. Missing edge restraint
Without a solid edge, pavers slowly spread outward. Gaps open up, sand washes out, and the field of pavers loosens and dips.
What a proper interlock build looks like
Utility locates through Ontario One Call before any digging.
Excavation to the right depth for the use: patio, walkway or driveway.
Grading the subgrade so water drains away from the house.
Granular base installed and compacted in lifts.
Bedding layer screeded perfectly level and to slope.
Pavers laid in pattern, with clean cuts at edges.
Edge restraint fastened along all open edges.
Polymeric sand swept into joints and activated to lock pavers together and resist weeds.
Can sunken interlock be fixed?
Often, yes. If the pavers are in good shape, a section can be lifted, the base rebuilt and compacted, and the same pavers relaid. The key is fixing the cause, whether that's depth, compaction or drainage, not just topping up sand.
If a large area has failed, it's usually more cost-effective to rebuild properly than patch it every spring.
Questions to ask any interlock contractor
How deep will you excavate for this project?
How do you compact the base, and in how many lifts?
Where will the water go?
What edge restraint do you use?
What does your warranty cover, and for how long?
At Klutch Landscaping, we're certified installers with the Interlocking Concrete Pavement Institute (ICPI), and all our hardscape work carries a three-year workmanship warranty.
See our interlock and stone work, or book a consultation if your interlock needs attention.
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