Why Are My Interlock Stones Sinking or Shifting? A Guide to Interlock Repair

You invested in a beautiful interlock driveway. It looked perfect when it was installed. Now some stones are sinking. Others are shifting out of place. Gaps are appearing. What went wrong?

This is frustrating. But here’s the good news: sinking and shifting stones are rarely the stones’ fault.

The real problems happen beneath the surface. Understanding what’s causing the damage is the first step toward a permanent fix.

In Vaughan, Richmond Hill, and across the GTA, these issues are common. And in Canadian weather, small shifts become big problems fast. One freeze-thaw cycle can turn minor settling into major structural damage.

Let’s look at the five main causes—and how professional repair fixes each one.

Cause #1: Poor Base Preparation

This is the most common reason interlock fails.

Your stones sit on layers of material underneath. Compacted gravel forms the foundation. Bedding sand creates the final level surface. If these layers weren’t done right during installation, problems develop.

What goes wrong:

• Excavation wasn’t deep enough
• Gravel layers weren’t compacted properly
• Bedding sand was uneven
• Contractor used cheap materials

What you see:

Dipping where car tires travel. Rutting along the path you drive every day. Stones that sink lower than their neighbors.

Why it matters in the GTA:

Soil types vary across Markham, Aurora, and surrounding areas. A “one-size-fits-all” base doesn’t work everywhere. Without a solid foundation built for local conditions, stones have nothing holding them in place.

Cause #2: Water and Freeze-Thaw Damage

Water is your interlock’s worst enemy.

When water seeps between stones and reaches the base layer, it softens the foundation. That’s bad enough. But in Ontario, it gets worse.

Here’s what happens in winter:

Water trapped under your stones freezes overnight. Ice expands by about 9%. That expansion pushes stones upward with massive force.

Then temperatures rise. Ice melts. Stones settle back down—but not where they started.

The cycle repeats:

This freeze-thaw process happens dozens of times each winter. Every cycle moves stones slightly. By spring, your once-level surface has become uneven.

The solution:

Interlock sealing creates a barrier that keeps water out of the joints. No water getting in means no ice pushing things apart.

Cause #3: Joint Sand Failure

See the sand between your stones? It’s not just filling gaps. It’s holding everything together.

Joint sand acts like glue. It stops stones from rubbing against each other. It prevents lateral movement. It keeps your driveway locked in place.

What happens when sand fails:

🔹 Heavy rain washes it away
🔹 Power washing blasts it out
🔹 Time and traffic wear it down
🔹 Joints become empty

Once joints are empty:

Stones lose stability. They start “creeping” apart. Gaps widen. The whole system loosens.

Weeds make it worse:

Empty joints invite weeds. Roots grow down into the base. They push stones apart from below. More gaps mean more weeds. The cycle accelerates.

Modern solution:

Polymeric sand hardens when activated with water. It stays in place much longer than regular sand. Professional maintenance includes cleaning out old joints and installing fresh polymeric sand to lock everything together again.

Cause #4: Drainage Problems

Sometimes sinking happens in one specific area. Usually near the drain.

What’s happening:

Your driveway should slope toward the catch basin. Water flows there, enters the drain, and exits your property. Simple.

But if your catch basin clogs or collapses, water has nowhere to go. It pools on the surface. Then it finds its way under the stones.

The result:

Standing water erodes bedding sand. The area around your drain sinks. Stones dip into a bowl shape. More water collects there. Damage accelerates.

Why surface repairs don’t last:

You can re-level the stones around your drain. But if the drainage problem isn’t fixed, water will erode the base again. You’ll be back where you started within a year.

The real fix:

Professional catch basin repair solves the underlying issue. Once water drains properly, surface repairs become permanent.

Cause #5: Heavy Vehicle Damage

Interlock handles cars well. But heavier vehicles cause problems.

Damage sources:

• Delivery trucks parking on your driveway
• Moving vans sitting for hours
• Construction equipment during renovations
• Heavy trailers or boats stored long-term

What happens:

Concentrated weight compresses the base in specific spots. Stones sink where the heavy load sat. Surrounding stones stay higher. Uneven surface develops.

Prevention:

If you expect heavy vehicles, let contractors know during installation. A reinforced base handles more weight. For existing driveways, avoid parking heavy loads in the same spot repeatedly.

How Professional Repair Fixes These Problems

Here’s the good news about interlock. Unlike asphalt, you don’t need to replace everything.

Interlock is modular. Problems can be fixed piece by piece. Only the damaged section needs attention.

Local Experts Across the GTA

No Limit Sealing understands the unique challenges GTA weather creates for interlock surfaces. We provide expert repair and maintenance throughout the region.

Our services include:

• Interlock repair and releveling
• Professional sealing
• Polymeric sand replacement
• Catch basin repair
• Full restoration services

Areas we serve:

🔹 Vaughan and Richmond Hill
🔹 Markham and Aurora
🔹 Toronto and Newmarket
🔹 King City and surrounding GTA communities

Don’t Wait for Small Problems to Become Big Ones

Your interlock is durable. But it needs professional attention when problems appear.

Minor shifting today becomes a tripping hazard tomorrow. Small dips become large sinkholes after another winter. Easy repairs become expensive reconstructions when you wait too long.

Contact No Limit Sealing today for a professional assessment.

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We’ll identify exactly what’s causing your sinking or shifting. We’ll fix the root problem—not just the symptoms. And we’ll protect your repair against future damage.

Call now and restore your interlock to its original beauty. 

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