Interlock Repair in Ottawa: Relay the Pavers or Rebuild the Base?

A sunken section of interlock does not automatically mean the entire patio, walkway or driveway needs to be rebuilt. Sometimes the problem is limited to a few pavers and the material directly beneath them. In other cases, the visible dip is surface evidence of a failing base or unstable soil.

The difference matters. A local lift-and-relay repair can be sensible when the surrounding pavement is stable. If the base is soft, poorly compacted or being eroded by water, simply raising the pavers may produce a repair that looks good temporarily and then sinks again.

To choose the right repair, examine the pattern of movement, inspect the site for drainage problems and, when necessary, lift enough pavers to see what is happening underneath.

This article applies to conventional concrete pavers installed on bedding sand over a compacted aggregate base. Permeable interlocking pavement uses a different assembly and should be assessed separately.

Start With the Pattern of Damage

The shape and location of the problem can provide useful clues.

One or two low pavers in an otherwise flat patio may indicate a small bedding defect or confined settlement. Two long depressions along the tire paths of a driveway suggest that the pavement is losing support under repeated vehicle loads. A dip beside a downspout raises an immediate drainage question.

What you see	What may be happening
A few isolated low pavers	Local bedding or base settlement
A depression beside a downspout	Erosion or repeated saturation
Ruts where vehicle tires travel	Insufficient base depth, poor compaction or weak soil
Broad waves across a patio	Settlement affecting a larger part of the base
A raised area that changes with the seasons	Frost-related soil movement or trapped moisture
Pavers spreading near the perimeter	Failed or poorly supported edge restraint
One cracked paver	A damaged unit, unsupported corner or concentrated load
A repaired area that keeps sinking	The earlier repair did not reach the failed layer or correct the cause

These observations are a starting point, not a complete diagnosis. A photograph can show where the pavement moved. It cannot show the thickness, moisture or condition of the material below it.

What Is Under an Interlock Patio or Driveway?

A typical sand-set interlock installation consists of:

1. Concrete pavers
2. Joint sand between the pavers
3. A thin bedding layer
4. A compacted aggregate base
5. Prepared soil, known as the subgrade
6. Edge restraints around the pavement

Each layer has a specific job.

The bedding sand creates a consistent surface on which the pavers can be placed. It should not be used to compensate for a base that is low or uneven. Adding a thick mound of sand beneath a sunken paver may restore its height temporarily, but the extra material can compress or migrate, allowing the paver to settle again.

The Concrete Masonry & Hardscapes Association construction guide calls for a nominal 25 mm uncompacted bedding layer. It advises repairing low areas in the aggregate base with base material and compacting them before restoring the bedding layer.

As general guidance over well-drained soil, CMHA identifies approximately 100 mm of compacted aggregate base for patios and pedestrian areas and at least 150 mm for residential driveways. Those measurements are starting points, not universal specifications. Soil strength, drainage, climate and expected traffic can all change the required design.

That distinction is important in Ottawa, where freezing temperatures and changing freeze-thaw conditions place additional demands on pavement construction and drainage.

When a Local Lift and Relay Is Usually Enough

A local repair is a reasonable option when the affected area has a clear boundary and the pavement around it remains firm and properly graded.

A section may be suitable for relaying when:

• Only a few pavers have moved.
• The surrounding surface has remained stable.
• There is no continuing source of water entering the area.
• The nearby edge restraint is secure or can be repaired locally.
• The material below the affected section can be rebuilt against a stable base.
• The existing pavers are in good enough condition to reuse.

A proper relay involves more than lifting the pavers and adding sand.

The contractor should remove enough pavers to expose the full extent of the weak area. Loose, contaminated or unsuitable material should be removed, and any problem with drainage or edge restraint should be corrected. The aggregate base can then be restored in layers that can be compacted properly, followed by a consistent bedding layer.

The pavers are relaid to match the surrounding pattern, elevation and slope. The repaired area is then compacted and the joints are refilled with suitable joint material.

CMHA’s operation and maintenance guide for interlocking concrete pavement recommends using the undisturbed surrounding pavement to re-establish the correct grade. It also warns against using bedding sand to correct low areas in the base.

Older pavers can often be cleaned and reused. This usually provides a better visual match than installing new units. If replacements are needed, confirm their availability before opening a large area. Even when the original product is still manufactured, new pavers may differ from units that have weathered for years.

When the Base Needs to Be Rebuilt

A surface-level repair is less likely to last when the movement is broad, recurring or associated with vehicle loads.

A deeper repair may be needed if:

• Several sections are settling in different places.
• A large portion of the patio has developed dips or waves.
• Driveway ruts return after the pavers are relaid.
• The exposed base is wet, soft or mixed with soil.
• The pavement was installed over poorly compacted fill.
• Water continues to flow through or beneath the damaged section.
• The edge has moved far enough to disrupt the laying pattern.
• The existing slope does not allow water to drain properly.
• A previous repair has failed in the same location.

In these situations, the work may involve removing a larger section and excavating until stable material is reached. The base can then be reconstructed in properly compacted layers.

Areas beside steps, curbs, walls, foundations and utility structures deserve particular attention. Large compaction equipment cannot always reach these locations, which can leave pockets of weaker material. CMHA recommends achieving the required compaction beside edges and structures rather than judging the base only by its appearance.

It is rarely possible to specify the exact excavation depth from a surface inspection alone. The required depth depends on the soil, drainage, traffic and existing materials found after the pavement is opened.

Address Drainage Before Closing the Repair

Water does not cause every interlock problem. However, when water repeatedly reaches a failed area, its source and route should be investigated before the pavers are relaid.

Inspect the area during rain or shortly afterward. Look for:

• Water collecting on the pavement
• Runoff crossing the damaged section
• A downspout discharging nearby
• Erosion beside an edge
• A lawn or garden sloping toward the pavement
• A blocked swale or catch basin
• Wet, soft material below lifted pavers
• Base material that moves or forces water and fine particles upward under pressure

The repair should respond to the actual source of water. That may mean redirecting a downspout, restoring a blocked drainage route, repairing an eroded edge or adjusting the surface grade.

Subsurface drainage may be appropriate in some situations, but it needs a clear purpose and a suitable outlet. A French drain is not a universal cure for a sinking patio. Without a proper outlet or a clear understanding of the site, it may collect water beside the pavement or transfer the problem elsewhere.

The City of Ottawa’s lot-grading guidance advises property owners to preserve the intended drainage of their lots. Downspouts should discharge onto the owner’s property, toward a permeable area and away from the foundation. Water should not be directed onto a neighbouring property, sidewalk, right of way or easement.

Any proposed grading or drainage changes should be checked against current municipal requirements before work begins.

Raised Pavers Need a Diagnosis Too

In Ottawa, raised interlock is often blamed on frost heave. That may be the cause, but it is not the only possibility.

Roots, debris beneath a paver, excessive bedding material, a moving edge restraint or an uneven base can all create a high spot. Sometimes the surrounding pavement has settled, making one stable section appear raised.

Seasonal behaviour is an important clue. If the same area rises during winter and changes again after the ground thaws, the repair should account for moisture and soil movement. Resetting the pavers during summer without addressing those conditions may not solve the problem.

A single high paver may have a simple local cause. A broad area that moves repeatedly deserves a deeper investigation.

Wide Joints Often Point to a Failed Edge

Interlocking pavement relies on edge restraints to prevent the pavers from spreading. When an outside row begins moving outward, the joints behind it can widen and the laying pattern may gradually lose alignment.

Signs of an edge problem include:

• Gaps increasing near the pavement perimeter
• Edge pavers leaning or moving outward
• Repeated loss of joint material in the same location
• A laying pattern that no longer lines up
• Pavers dropping beside a failed edge
• Loose or displaced edging

Adding more joint sand will not stabilize a moving edge. The restraint must be repaired or replaced and supported by the compacted base rather than sitting loosely in bedding sand.

CMHA describes edge restraints as an essential part of interlocking concrete pavement because they resist the horizontal forces that would otherwise allow the units to spread.

Once the edge is stable, the pavers can be returned to the correct spacing and elevation. The surface can then be compacted and the joints refilled.

The same principle applies to polymeric sand elsewhere in the pavement. It is a joint material, not a structural repair. It cannot replace missing support beneath a sunken paver.

Questions to Ask Before Approving a Repair

A useful estimate should describe what the contractor intends to do below the surface, not only how many square feet of pavers will be lifted.

Ask the contractor:

• Which layer appears to have failed, and what evidence supports that conclusion?
• Will enough pavers be lifted to inspect the base?
• How far will the repair extend beyond the visible depression?
• What material will be used to rebuild the base?
• In what thicknesses will the material be placed?
• How will each layer be compacted and verified?
• Is water contributing to the damage?
• Where will runoff go after the repair?
• Will damaged edge restraints be replaced?
• Can the existing pavers be reused?
• How will replacement pavers be matched?
• What happens if weak soil or a settled utility trench is uncovered?
• What recurring settlement, if any, is covered by the warranty?

The City of Ottawa states that businesses installing, altering or paving hard landscaping features, including vehicular or pedestrian access, must be licensed as hardscaping contractors. Homeowners can review the City’s current driveway, walkway and hardscaping rules before hiring a contractor.

Before any excavation begins, obtain underground utility locates through Ontario One Call. Provincial law requires locates before digging, including work performed with hand tools. Landscaping and hardscaping can encounter buried gas, electrical and communications lines as well as water and sewer infrastructure.

The Practical Decision

Choose a local lift and relay when the damage is confined, the surrounding pavement is stable and the cause can be corrected within a defined area.

Consider deeper reconstruction when the movement is widespread, keeps returning, follows vehicle wheel paths or is connected to unresolved drainage.

The visible pavers show where the failure appeared. A lasting repair depends on finding where it started.

For an on-site assessment, contact Ottawan Landscapers about interlock repair in Ottawa. If the damaged area is also affected by standing water, downspouts or poor lot grading, ask about grading and drainage services in Ottawa before the pavers are relaid.