The foundation of pavers typically consists of multiple layers, including a compacted subgrade, a granular base, and a sand bedding layer. These materials work together to provide stability, drainage, and longevity for paver installations. The specific materials used include crushed rock for the base, concrete sand for the bedding layer, and specialized joint sand for filling gaps between pavers.
What are the Key Components of a Paver Foundation?
A proper paver foundation consists of several layers, each serving a specific purpose:
- Compacted Subgrade
- Granular Base
- Sand Bedding Layer
- Pavers
- Joint Sand
Let’s explore each of these components in detail.
What is the Purpose of the Compacted Subgrade?
The compacted subgrade is the foundation upon which all other layers rest. It serves several crucial functions:
- Provides a stable base for the entire paver structure
- Ensures proper drainage
- Prevents settling and shifting of the pavers over time
To prepare the subgrade:
- Excavate the area to the required depth
- Remove any organic material or debris
- Compact the soil to 100% of the corrected maximum dry density
- Create a slight slope (typically 1 inch every 4 feet) for water drainage
What Material is Used for the Granular Base?
The granular base is a critical component of the paver foundation. It typically consists of:
- Crushed rock (3/4 minus gravel)
- ‘Crusher Run’ limestone gravel
Specifications for Granular Base Material:
| Sieve Size | Percentage Passing |
|---|---|
| 25 mm | 100% |
| 16 mm | 75-95% |
| #4 | 35-55% |
| #16 | 15-35% |
| #50 | 7-20% |
| #200 | 3-10% |
The granular base should be:
- Clean and free from shale, clay, and organic matter
- Hard and durable
- Compacted in layers using appropriate equipment
Recommended Base Thickness:
- Pedestrian areas: 6 to 8 inches (16-20 cm)
- Vehicular areas (established): Minimum 8 inches (20 cm)
- Vehicular areas (new developments): 10 to 12 inches (25-30 cm)
What Type of Sand is Used for the Bedding Layer?
The sand bedding layer is crucial for creating a smooth, level surface for the pavers. The material used is:
- Concrete sand
Specifications for Bedding Sand:
- Thickness: 1 to 1.5 inches
- Less than 1% passing the 75 µm sieve
- Free of organics and deleterious soluble salts
- Free of contaminants
What is Joint Sand and Why is it Important?
Joint sand is used to fill the gaps between pavers, providing stability and preventing weed growth. It should:
- Meet the gradation requirements of mortar sand
- Meet the physical requirements of concrete sand
- Be dry and free of contaminants
When is a Concrete Foundation Used Instead of Granular Base?
In some cases, a concrete foundation may be used instead of a granular base. This is typically done in areas with:
- Heavy traffic
- Poor soil conditions
- Specific design requirements
When using a concrete base:
- Construct according to OPSS 350 standards
- Ensure the concrete mix meets specific strength and durability requirements
- Follow contract documents and relevant construction standards
What are the Best Practices for Installing Paver Foundations?
To ensure a long-lasting and stable paver installation, follow these best practices:
- Proper Drainage: Create a gradient or slope to prevent water pooling
- Compaction: Use appropriate equipment for each layer
- High-frequency, low-amplitude mechanical flatplate vibratory compactor for bedding sand
- Pneumatic-tired roller for granular base and subgrade
- Material Selection: Choose materials that meet specified gradation and physical requirements
- Systematic Installation:
- Excavate
- Lay base material
- Place sand layer
- Install pavers
- Compact and level each layer before proceeding
What are the Typical Costs for Paver Foundation Materials?
Costs can vary depending on location, material type, and labor, but here are general estimates per square foot:
- Granular base material: $1 to $3
- Sand layer: $0.50 to $1.50
- Pavers: $3 to $15 (varies by type and quality)
- Labor costs: $2 to $5
Conclusion
The foundation of pavers is a complex system of layers, each serving a specific purpose. By using the correct materials and following proper installation techniques, you can ensure a stable, long-lasting, and beautiful paver surface.
References:
1. OPSS.PROV 355
2. Oregon State University Extension
3. Unilock