When it comes to installing any durable and long-lasting pavement, the base is one of the most crucial elements. A poorly prepared base can lead to several issues, such as uneven pavers, shifting, and other costly repairs. This article discusses the importance of a proper paver base, the minimum necessary depth for different applications, and the best materials to use for a solid foundation.
Why it Matters
The paver base is the foundation that supports the pavers, preventing movement, providing stability, ensuring a level surface, and a long life. This is especially important in areas with heavy traffic loads, such as driveways or commercial parking lots. If these problems occur, the only long-term solution involves removing the pavers, bedding layer, and base, excavating deeper, and rebuilding the entire pavement structure. A key advantage of using interlocking concrete pavers, unlike asphalt or poured concrete, is that the pavers themselves can be reused during these base repairs.
Choosing the Right Base Material
The base material can determine the success or failure of a pavement. But factors such as cost and often more importantly, the availability of good material play a key role. Aggregates approved for use as road base by the local city and state/province department of transport, owned roads are appropriate for interlocking concrete pavements and are available from most stone quarries or suppliers. But if your project is in an aggregate “desert”, keep these guidelines in mind.
- Ask the quarry/supplier if they have anything close to the gradation as the bases used by the local municipalities.
- Check with the quarry/supplier if they have anything close to the grading requirement for dense graded aggregates (DGA) per ASTM D2940 as shown in Table 1.
- Never use stone dust or screenings.
- Don’t use rounded or smooth aggregates, such as river rock or pea gravel.
- Stay away from anything that has a lot of small particles, dust, finer than sand.
You might be wondering about open-graded aggregate (OGA), clean 57 stone, no-fines aggregate, hybrid bases, or whatever term you use. Are they the right choice for a base? Well, they do have a place as the right base, and CMHA is developing best practice guidelines for OGA. However, for standard paver installation, OGA is not recommended for vehicular applications, and if used for a patio, homeowners should be informed that they may need to replenish the joint sand from time to time.
What Depth Should The Base Be?
First it is important to define ideal conditions.“Ideal conditions” can be defined as the most favorable or best possible circumstances for a specific purpose or outcome, essentially representing the optimal state for something to happen or be achieved. The ideal condition for a pavement is to have a subgrade that is strong, structurally sound, and well-draining in a continuously stable climate, preferably a non-freezing warmer climate.
The minimum base depth also depends on the application and expected load. The heavier the load, the thicker the base. Here are the recommended minimum base thicknesses for ideal conditions.
- Walkways, Patios, Pedestrian: 4 inches (100 mm)
- Residential Driveways: 6 inches (150 mm)
- Parking Lot/Residential Street: 8 inches (200 mm)
- Streets and Heavy-Duty Industrial Pavements: No minimum – consult a qualified civil engineer
If your project is not in an ideal location, with weak soil, poor drainage or areas that freeze, you will want to increase base thickness. If you want to be sure of your design or that the thickness of your base is correct, check out the design tables in CMHA’s Tech Note 4, Structural Design of Interlocking Concrete Pavement for Roads and Parking Lots.
As a quick estimate, you can increase the recommended minimum base thickness by 50% for each of the three optimum conditions that don’t exist on your site. Strength. Drainage. Freezing. As an example, for a driveway where none of the optimum conditions exist a rough guess would be 15 inches (6+3+3+3) or 375 mm (150+75+75+75).
Other Common Mistakes
Insufficient compaction. Proper compaction sets your base up to last a long time, increases the density and stability, reducing settlement and to withstand any heavy loads. A plate compactor smaller than 5,000 pound force is too small, also, don’t believe the myth; OGA does need to be compacted after it has been placed.
Do it Right, Do it Once
A strong and well-prepared paver base is essential for the longevity and performance of your installation. By choosing the right materials, ensuring the proper depth, and following best installation practices, you can create a beautiful, durable surface that’ll envy everyone who sees it and will stand the test of time.
Under or over-excavation. Under excavation can lead to thin bases, and possible settling or rutting in the future. Over excavation leads to extra time, material and cost. Use best practices, design guides, and proper surveying tools to get the right depth.
Not allowing proper drainage. Poor drainage can lead to a long list of maintenance issues. Efflorescence, staining, mold, and eventually uneven settling and rutting. Pay attention to the water flow and where it goes. In particular, OGA needs an outlet for any water that enters the aggregate.
Are you planning a paver project? Explore our technical resources to assist with your next project.
About the Author
Bryan Horr, P.E.
CMHA Division Engineer, Segmental Pavements
Bryan Horr, P.E., a seasoned Civil Engineer with years of hands-on construction expertise, seamlessly blends practical field experience with theoretical knowledge. Currently serving as the Divisional Engineer for Segmental Pavements at CMHA, Bryan leverages his construction background to impart valuable insights in the classroom. Having instructed numerous contractors in the CMHA Concrete Paver Installer Course and the PICP Specialist Course, he devotes a significant portion of his time to educating design professionals about the advantages of using interlocking concrete pavers as a superior pavement solution. Connect with Bryan on LinkedIn.