Why open-graded, washed stone works
Clean, angular aggregate forms large, connected voids that move water fast while interlocking for stability. The angular faces lock under compaction, so the base resists rutting and wave formation under foot traffic and play. Washed stone keeps fines out, preserving permeability over time.
- High flow rate: continuous voids evacuate rain quickly.
- Stable platform: angular interlock resists movement.
- Clean system: minimal silt migration that could clog the base.
Recommended aggregate specs
Primary base layer
Use an open-graded, washed, angular stone commonly specified as No. 57. It seats well under compaction and delivers strong flow capacity for most landscapes and sports areas.
Optional choker or leveling layer
Top the base with a very thin layer of smaller clean stone, often called No. 89, to fine tune grade and smooth high spots without killing permeability. Keep it thin, about 0.5 to 1 inch.
What to avoid
- Pea gravel: rounded particles move and create a slippery base.
- Screenings, stone dust, or limestone fines: trap water and cement when wet, reducing drainage.
- Mixed, unwashed road base: fines migrate into fabrics and soil, clogging the system.
Base depth and slope
- Typical lawns and play areas: 3 to 4 inches of open-graded base.
- High use, pets, or wet soils: 4 to 6 inches.
- Freeze-thaw or heavy rainfall regions: add 1 to 2 inches and prioritize separation fabric.
Pitch the base 1 to 2 percent away from structures. Even permeable systems work better with a consistent surface slope.
Separation and stabilization
- Install a nonwoven geotextile over subgrade to separate soil from stone and reduce pumping.
- On soft or saturated subgrades, add a biaxial geogrid under the base to limit settlement.
Installation steps
- Excavate organic soil to required depth plus turf thickness. Proof roll to spot soft areas.
- Shape subgrade to 1 to 2 percent slope and remove loose debris.
- Lay nonwoven geotextile with 12 inch overlaps, pinned flat.
- Place open-graded base in 2 inch lifts. Compact each lift with a plate compactor. The goal is stone seating and interlock.
- Add a 0.5 to 1 inch clean-stone choker only if needed to perfect grade.
- Check elevations, crown or crossfall, and edge restraints. Install turf per spec.
Drainage upgrades for tough sites
- French drain tie-ins: run perforated pipe at the low side of the base and outlet to daylight or a dry well.
- Edge relief: leave a small gap behind curbs or install weep holes to avoid trapped water.
- Downspout management: divert roof runoff away from the field to reduce peak loads.
Regional notes
- Cold climates: increase base thickness and use nonreactive aggregates that do not create fines under freeze-thaw.
- Clay soils: prioritize separation fabric and consider geogrid. Avoid fines at all layers.
- Coastal or high groundwater: ensure an outlet or storage layer below grade if your water table is shallow.
Compatibility with infill and pads
Clean, open-graded bases work with silica sand, coated infills, and performance pads. A firm, uniform base improves ball roll and foot traction while keeping drainage active through the entire system.
Material checklist
- Nonwoven geotextile for separation
- Open-graded angular stone for base
- Small clean stone for optional choker
- Edge restraints and pins
- Plate compactor and laser or stringline for grade control
Common mistakes to avoid
- Using rounded pea gravel that shifts under load
- Building with crusher fines or screenings that hold water
- Skipping geotextile on clay or silty soils
- Zero slope surfaces that invite ponding
- Over-thick choker layers that reduce permeability
