The Size of Patio Base Stones

Large Gravel

• Large gravel measures from 1-1/4 inches to about 3 inches. If the patio site has dense, clay-like soil, the bottom of the base should be laid with a 4-inch-thick layer of large gravel about the size of a golf ball. The large rocks leave more space between them for water to escape, preventing frost heaves and water damage to the foundation. If the subsoil still feels soft once compacted, pin down geotextile fabric, before laying the base, to prevent the rocks and pavement from sinking.

Medium Gravel

• Medium gravel offers an almost solid base with smaller spaces for draining water to travel through. Between 3/4-inch and 1-1/4 inches in size, these angular rocks are a good fit for well-drained soil or on top of a layer of larger gravel. Sharp edges and irregular shapes allow medium gravel to wedge snugly together when compacted in 3- to 4-inch-thick layers at a time.

Small Gravel

• Small gravel averages about 3/8-inch, but it can break down into smaller pieces with a sand-like consistency. This material is typically used as a top layer on gravel driveways because it forms a stable, compact surface under pressure. While it’s water-permeable, smaller pieces fill many of the spaces so water doesn’t drain as quickly as it does through larger gravel. Use small gravel as the bottom layer of the base if the soil feels sandy because the patio will need the extra support.

Stone Dust

• Stone dust is used to fill the joints between patio pavers. When moistened, it naturally hardens to gravel and other surrounding materials as it dries. For a patio base, stone dust can stabilize medium gravel. Pour it over the top layer of a gravel base to fill in the gaps between stones and provide a leveling bed for dry-setting flagstones and other types of paving materials.