What Is An Interlocking Paver Base? (Subbase Specs)
An interlocking paver base is the compacted aggregate foundation beneath the bedding sand and pavers. It spreads loads, supports the surface, and helps water drain. Its thickness depends on traffic, soil, moisture, and frost exposure. Common starting points are 4–6 inches for walkways and 6–8 inches or more for residential driveways, subject to the project design.
Paver projects can look simple from above, but much of their strength comes from layers you cannot see. A base that is too thin, loose, or wet may settle unevenly. The result can be rocking pavers, open joints, or a raised edge that becomes a trip hazard.
I often find that the term “paver base” causes confusion because people use it for both the aggregate foundation and the whole layer system. Below, I’ll separate those parts, explain common specifications, and show how to check that the design fits the site. Always follow the project documents and the paver and aggregate suppliers’ instructions where they set different requirements.
Base Design, Materials & Site Safety
An interlocking paver base is a compacted layer of aggregate below the bedding course. Together, the base and bedding support the pavers, but they do different jobs: the base carries and spreads loads, while the thin bedding layer helps set the pavers to line and grade.
What layers make up a paver foundation?
A typical installation has prepared soil, compacted aggregate base, bedding sand, pavers, and joint material. Edge restraints hold the outside pavers in place. The base is not the same as the bedding sand, and the bedding sand is not a substitute for a weak or uneven base.
| Layer | Common material or dimension | Main job |
|---|---|---|
| Subgrade | Prepared, compacted native soil or approved fill | Supports the layers above |
| Aggregate base | Dense-graded crushed aggregate; often specified to ASTM D2940 | Spreads loads and provides a stable foundation |
| Bedding course | About 1 in (25 mm) of clean, hard concrete sand; project gradation may reference ASTM C33 | Provides a uniform setting layer |
| Pavers | Often 60 mm for pedestrian areas and 80 mm for vehicle areas | Forms the finished surface |
| Joint material | Compatible joint sand or specified product | Fills joints and helps limit paver movement |
These are common references, not automatic rules for every site. Confirm the specified aggregate gradation, bedding material, and paver thickness for your project. Clean, uniformly sized stone may drain well, but it does not compact like dense-graded aggregate and should not replace it unless the design calls for that system.
How thick should the base be?
Base thickness is the compacted depth of the aggregate, not the depth of the bedding sand or pavers. Typical starting ranges are 4–6 in (100–150 mm) for pedestrian areas and 6–8 in (150–200 mm) or more for residential driveways. Weak or wet soil, heavy vehicles, and frost exposure may require more depth or an engineered design.
| Use or condition | Common starting point | What may change the design |
|---|---|---|
| Walkway or patio | 4–6 in (100–150 mm) compacted base | Soft soil, water, frost, or local requirements |
| Residential driveway | 6–8+ in (150–200+ mm) compacted base | Vehicle weight, soil strength, drainage, and climate |
| Weak, wet, or frost-prone ground | No single safe thickness | Soil assessment and project design are important |
The paver thickness itself does not determine the base depth. A thicker paver cannot make up for a poorly supported foundation. For a vehicle area, check that both the paver and the base design suit the expected traffic.
What materials and safety checks matter?
Dense-graded crushed aggregate contains a range of particle sizes, from larger pieces to fines. When placed and compacted, those sizes lock together. The project specification may reference ASTM D2940, but the exact grading and local requirements still matter.
Before digging, locate underground utilities through the appropriate local service. Plan the finished elevations and a route for runoff. Use equipment suited to the work area, follow its manual, and wear the protective gear it calls for. Keep people clear while a plate compactor is running. Use a protective mat when compacting over installed pavers to reduce the risk of scuffing or damaging their surface.
Excavation, Compaction & Paver Installation
Installation works best when each layer is prepared before the next one hides it. Set the grade, stabilize the soil, compact aggregate in controlled lifts, and keep the bedding course even. A thick layer placed all at once may not compact through its full depth.
How do you set the excavation depth?
Excavate for the full build-up: compacted base, bedding course, and paver thickness. Also account for the finished elevation at doorways, paths, drains, and edges. A simple depth check is to add the specified compacted base depth to the bedding and paver thickness, then confirm the result against the planned grade.
For example, a design using a 6 in (150 mm) compacted base, 1 in (25 mm) bedding course, and 60 mm pavers needs roughly 9.4 in (240 mm) from the top of the base area to the finished surface. This is a planning example, not a universal excavation depth. The base may need a different thickness, and actual excavation depends on the existing ground and grading plan.
Shape a consistent fall so water moves away from buildings. A common surface slope is 1.5–2%, where the surface drops 1.5–2 units for every 100 units of horizontal distance. Confirm the slope and drainage outlet for the site rather than directing runoff toward a building or neighbor.
How should the base be placed and compacted?
Remove topsoil, roots, and soft or organic material. Shape and compact the subgrade. If the soil moves, pumps water, or feels unstable under equipment, stop and correct the problem before placing aggregate. A geotextile may be appropriate in some designs or soil conditions, but it is not a cure for every weak subgrade.
Place aggregate in lifts no thicker than about 4 in (100 mm) loose, then compact each lift. Add or reduce moisture as needed for the material and the project requirements. A common project target is at least 95% of maximum dry density under ASTM D698, but targets and test methods vary. Check the specification instead of assuming that 95% applies to every job.
After compaction, inspect the base for soft spots and uneven areas. Do not cover a defect with extra bedding sand. Bedding sand is usually screeded to about 1 in (25 mm), kept uniform, and left uncompacted before the pavers are laid. Walking on it or using it to correct dips can create uneven support.
What is the correct paver installation sequence?
Once the base and bedding course are ready, lay pavers to the planned line and grade. Install the specified edge restraints; without firm edges, pavers can spread and joints may open. Compact the finished pavers with an appropriate machine and protective mat, following the paver maker’s instructions.
Sweep compatible joint sand into the joints, compact if required, then fill the joints again as needed. Check the finished surface for stable pavers, full joints, secure restraints, and a clear route for runoff. Keep loose sand and debris out of drains.
A common field scenario is a patio where the aggregate looks level but has not been compacted in lifts. The surface may appear sound at first, yet later show dips or rocking pavers. Another is a driveway with a soft patch in the subgrade: adding more sand above it hides the problem, but does not restore support. In both cases, the reliable fix is to expose and correct the unstable layer.
Inspection, Joint Maintenance & Repairs
Inspection means checking both the surface and the conditions beneath it. Look for changes in paver height, open joints, water that remains after rain, and edges that have moved. These clues can point to a drainage, restraint, or support issue, but the visible symptom alone may not reveal the cause.
What should you check before and after installation?
Before laying pavers, verify that the excavation reaches the planned depth and that the subgrade is stable. Check aggregate thickness by lift and confirm compaction against the project specification. If a density test is required, use the specified method and target.
After laying, check that the pavers are supported, joints are filled, edges are restrained, and water has a reliable path away. If a section rocks or settles soon after installation, do not simply add joint sand and assume the issue is solved. Check for an unstable base, poor drainage, or a failed edge restraint.
How do you diagnose common paver problems?
| Sign | Possible cause to investigate | Practical next step |
|---|---|---|
| Rocking pavers | Uneven bedding, weak base, or lost support | Lift the affected area and inspect the layers |
| Repeated settlement | Poorly compacted base or unstable subgrade | Correct the weak layer; rebuild in compacted lifts |
| Washed-out or missing joint sand | Water flow, open joints, or maintenance needs | Identify the water path, then refill with compatible material |
| Water standing on the surface | Incorrect grade or blocked drainage route | Check elevations and the intended outlet |
| Pavers spreading at an edge | Missing or failed restraint | Inspect and repair the edge restraint |
These are diagnostic starting points, not certain diagnoses. If the area carries vehicles, has ongoing movement, or sits on saturated or very weak ground, have the design and site conditions assessed before rebuilding.
Drainage, Frost Protection & Long-Term Care
Drainage is part of base design, not a finishing detail. Water that collects in or below the pavement can soften soil, move fine material, or contribute to frost-related movement where freezing occurs. A sound base still needs suitable soil, grading, and an outlet for water.
How do drainage and frost affect base depth?
Surface slope should guide water away from buildings and toward a suitable outlet. A common slope is 1.5–2%, but the right grade depends on the site and local rules. Do not leave the finished surface without a reliable drainage path, and do not allow runoff to enter a drain that cannot handle it.
Frost conditions and wet soils can increase the risk of movement. A deeper base alone may not solve those conditions; soil type, water, local climate, and design all matter. Where freezing, poor drainage, or weak ground is a concern, use a project-specific design rather than treating a typical walkway or driveway depth as a guarantee.
What maintenance helps prevent movement?
Keep drains and surface channels clear so water can move as planned. Check the joints and edges from time to time, especially after heavy use or obvious water flow. Refill joints with a compatible material when needed, and address recurring washout rather than repeatedly replacing sand without finding the cause.
If pavers begin to rock, settle, or spread, inspect the layers and drainage before making a surface-only repair. A thick but poorly compacted base can still settle; a water-saturated base can lose support or erode. Correct the unstable soil, drainage, or compaction problem before rebuilding the surface.
The central rule is simple: use the specified compacted aggregate, build it in controlled lifts, and make the design fit the soil, traffic, and water conditions. Never lay pavers over topsoil, loose fill, or an inadequately compacted base.
Paver Base FAQ
These short answers cover common questions about paver base material, thickness, bedding sand, and compaction. Use them as general guidance, then check the project specification for the exact material, test method, and design depth required at your site.
Is paver base the same as paver bedding sand?
No. Paver base is compacted aggregate that supports and spreads loads. Bedding sand is a thin, uniform setting layer, commonly about 1 in (25 mm), directly below the pavers.
How deep should an interlocking paver base be?
A common starting range is 4–6 in (100–150 mm) for pedestrian areas and 6–8 in (150–200 mm) or more for residential driveways. Soil, water, traffic, and frost conditions can require a different design.
Can I use clean gravel instead of dense-graded base?
Not as a direct substitute when the design calls for compactable dense-graded aggregate. Clean, uniformly sized stone does not compact in the same way. Use the material named in the project specification.
How thick should each aggregate lift be?
A common limit is about 4 in (100 mm) loose per lift. Compact each lift before adding the next, and follow the project’s requirements for the aggregate and equipment.
What compaction level is required?
Some project specifications call for at least 95% of maximum dry density under ASTM D698. Confirm the target and test method for your project; requirements are not universal.
Should bedding sand be compacted before laying pavers?
Usually, it is screeded to a uniform depth and left uncompacted before the pavers are placed. Follow the paver system’s instructions, and do not use sand to hide an uneven base.
What slope should a paver surface have?
A common starting point is 1.5–2% away from buildings. Confirm the planned grade and outlet so runoff does not collect or flow somewhere unsuitable.
Can I put pavers directly over soil?
No. Remove topsoil and soft material, prepare and compact the subgrade, and install the specified base. Soil alone is not a reliable paver foundation.
What paver thickness is used for driveways?
Pavers around 80 mm thick are commonly used for vehicular areas, while 60 mm is common for pedestrian use. Confirm suitability with the manufacturer and project design.
Why are my pavers rocking or sinking?
Possible causes include uneven bedding, weak or poorly compacted base, unstable soil, water damage, or failed edge restraints. Inspect the layers and drainage before repairing the surface.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
