All About Open-Graded Cleanstone in Hardscapes: The Key to Resilient, Permeable Surfaces
Permeable hardscape installations rely on specific types of stone that support water infiltration and structural stability while resisting environmental stresses. Open-graded cleanstone, particularly angular varieties, is essential for permeable hardscape applications. Both the International Concrete Pavers Institute (ICPI) and the Concrete Masonry Hardscape Association (CMHA) recommend cleanstone as an optimal aggregate for permeable paving, due to its unique properties and technical advantages.
1. Characteristics of Angular Cleanstone
Angular cleanstone features sharp edges that create superior interlocking properties compared to rounded stone. When compacted, the edges of angular stone lock tightly, forming a stable, interconnected structure that resists displacement even under heavy loads. Cleanstone’s natural void space—approximately 50-55%—enables water to pass freely, aiding drainage and reducing stormwater runoff. ROMEX permeable jointing products, when installed with open-graded cleanstone, enhance these benefits, ensuring that water flows through the joints without risk of clogging.
2. Frost-Heave Resistance and Capillary Action Prevention
One major advantage of cleanstone is its resistance to frost heave and frost expansion. Frost heave occurs when soil beneath the stone freezes and expands, pushing the layers above it upward. Cleanstone resists frost heave by eliminating capillary action—the upward movement of water through fine particles—since the void spaces are too large to support this movement. This lack of capillary action prevents water from rising into the stone bed, meaning that when temperatures drop, there’s less water present to freeze and expand within the aggregate. This makes cleanstone an excellent choice for northern climates with frequent freeze-thaw cycles. For ultimate frost resistance, using ROMEX TRASS BED with cleanstone ensures that the aggregate layer remains stable and resilient in fluctuating temperatures.
3. Stability Through Compaction
Once compacted, cleanstone forms a stable base that does not compress further under load. Compacting the angular stone ensures each piece locks into place, creating a solid foundation that resists settling and shifting. Proper, thorough compaction helps create a fully locked, stable base with minimal movement. When paired with ROMEX permeable jointing mortars, this compaction supports both a structurally sound foundation and a resilient surface layer that can handle high-traffic loads without disruption.
4. Geo Fabrics and Geo Grids for Separation and Stability
Geo fabrics and geo grids should be used at the base of the cleanstone layer to prevent the soil below from mixing with the stone, preserving the cleanstone’s void spaces for water infiltration. These materials create a stable separation layer that keeps the subgrade from contaminating the aggregate, which helps maintain the structure’s load-bearing capacity. This separation also minimizes compaction issues related to soil shifting, especially in permeable systems, where water infiltrates and disperses. ROMEX installation guidance for permeable hardscapes often includes recommendations for these separation materials, ensuring that cleanstone layers remain uncontaminated, which is essential for optimal drainage and load stability.
5. Importance of a 1/4” Bedding Layer
The bedding layer should consist of no more than 1-2 inches of 1/4” cleanstone, providing an essential interface between the base layer and the paver surface. Using larger stone for bedding can compromise stability; 1/4” aggregate allows the layer to lock effectively under compaction, interlocking with the pavers above. This results in a stable, even surface that resists movement over time. ROMEX permeable bedding layers, particularly when combined with our jointing materials, provide additional support to pavers, securing them against the potential shifts and movement over time.
6. Managing the Choke Factor
The “choke factor” is the interlocking of various stone sizes, which stabilizes the structure. Cleanstone in the 1/4” to 3/4” range creates an ideal mix for permeable applications: smaller pieces fill gaps between larger stones, maximizing compaction and stability while preserving enough void space for drainage. ROMEX solutions work optimally with this cleanstone mix, as it helps maintain a high degree of permeability while also delivering essential compaction for stability.
Technical Specifications and Standards
According to ICPI and CMHA guidelines, open-graded cleanstone offers several critical advantages for permeable hardscapes:
- Void Space: 50-55%, providing ample drainage for stormwater management
- Angularity: Sharp, jagged edges allow for interlocking, increasing load-bearing capacity and stability
- Resistance to Frost Heave and Capillary Action: Large void spaces minimize upward water movement, reducing the risk of frost expansion and frost heave
- Non-Compressible: Once compacted, the stone remains stable and requires no further compression
- Bedding Layer: 1-2 inches of 1/4” cleanstone for even interlock with pavers
- Choke Factor: Use of a 1/4” to 3/4” cleanstone mix optimizes compaction and interlock without sacrificing permeability
Benefits of ROMEX and Open-Graded Cleanstone for Permeable Hardscape Systems
Using angular, open-graded cleanstone in conjunction with ROMEX permeable products leads to durable, sustainable surfaces that perform well in challenging climates. Cleanstone provides stability, supports environmental stewardship by facilitating water infiltration, and resists damage from frost and shifting soils. ROMEX solutions enhance these advantages, ensuring that hardscape professionals achieve long-lasting, resilient installations that support both load-bearing and environmental demands without compromising structural integrity.
