#8 Crushed Stone: Clean 3/32 to 3/8 Inch for Permeable Work

The most common reason people end up on this page is a surface that has stopped draining. A permeable patio or driveway was built with a bedding and joint material that carried fines in it, and for a season or two it worked. Then the fines settled, the joints closed, and rain began to sheet across the surface the way it does over concrete. #8 crushed stone is what the design called for in the first place: an angular aggregate of roughly 3/32 to 3/8 inch with little or no fine material, so the void space between the pieces stays open permanently.

Everything else on this page is about getting that material into the ground during the part of the year when the work will hold.

The working window: thaw to first frost across the north

Timing is not the same problem everywhere.

Across the frost belt the season is genuinely short. Open-graded bedding has to be placed and the units set before the ground freezes, because a base built into frozen or saturated subgrade settles unevenly as soon as it thaws. Late spring through early autumn is the practical window, and the early end of it is often too wet.

Across the sun belt and the desert southwest the calendar is nearly open, with the caveat that summer heat makes the labor brutal and late-summer storms can flood a half-finished excavation overnight. On the gulf and southeast coasts the deciding factor is the rainy season rather than the temperature: an open excavation during a wet week fills and softens, and the subgrade never recovers its bearing.

Preparation that has to be finished before the window closes

Work backwards from the day the pavers go down.

Excavate and shape the subgrade first, sloping it so that water leaving the stone reservoir has somewhere to go. Lay separation fabric against the walls and floor of the excavation on anything but clean sand. Build the open-graded base in lifts and settle each one before the next. Only then does the thin bedding course of this size go in, screeded to an even depth, followed by the units and the joint fill. Get the stockpile on site before the weather turns; a covered or hard-standing drop keeps mud and leaf litter out of a material whose entire value is its cleanliness.

Where #8 crushed stone earns its keep in a permeable build

• Permeable paver bedding and joints. The one job it is specified for above all others, bedding below and swept into the joints above.
• Drainage layers and reservoir courses. Open voids hold and release water under a surface that has to keep taking rain.
• Pipe bedding. Small enough to work in properly around a pipe barrel and support it evenly.
• Concrete mixes. Used where a small coarse aggregate is specified.
• A dry creek bed. As the working channel layer under or between larger decorative stone, where it keeps the flow moving instead of standing.
• A fire pit surround. Clean, angular and non-combustible, though it stays loose underfoot and is not a substitute for a hearth pad.
• A pole barn or equipment pad. As the free-draining layer under a slab, not as the surface a machine parks on.

Cubic yards for a 24 by 36 foot pad and a 30 foot creek line

Hypothetical figures. This site's calculator figures 3/8 inch chips at about 2,800 lb per cubic yard, or 1.40 tons per yard, so the tonnages below are approximate; the stone calculator will run the same conversion on your own dimensions.

Drainage layer under a pole barn slab. 24 by 36 feet at 4 inches: 24 x 36 = 864 square feet. 864 x 4 / 12 = 288 cubic feet. 288 / 27 = 10.67 cubic yards, and 10.67 x 1.40 = about 14.9 tons.

Dry creek channel. 30 feet long, averaging 4 feet wide, 4 inches deep: 30 x 4 = 120 square feet. 120 x 4 / 12 = 40 cubic feet. 40 / 27 = 1.48 cubic yards, or roughly 2.1 tons.

Fire pit surround. A ring 3 inches deep, 7 feet out from the center with a pit of 2.5 foot radius in the middle. Use the circle setting in the calculator with a 14 foot diameter and subtract the pit: the stone covers about 134 square feet, so 134 x 3 / 12 = 33.5 cubic feet, or 1.24 cubic yards, which is about 1.7 tons.

Keeping joints open and a creek line clean through the years

An open-graded system fails from the top down. Organic matter is what closes it: leaf fall, grass clippings, soil washed off a bed uphill, sand tracked in over winter. The upkeep is unglamorous and easy. Blow or sweep the surface before leaves break down, keep bare soil upslope planted or mulched so it stops arriving, and top the joints back up when they look low, since joint stone works its way down and out over the first year or two. In a dry creek line, lifting the decorative stone every few years and rinsing the channel layer restores most of the flow it had when new.

Ordering a clean stone and keeping it clean

Choose the tonnage and the delivery date on this page. Delivery is arranged at checkout by ZIP code, and the truck needs clear access to a spot it can tip on firm ground. Ask for the drop as close to the work as the access allows, on a hard surface if there is one, because the surest way to ruin an open-graded stone is to load it off bare soil in wet weather. If you are building to a permeable paver detail and want your layer volumes checked, send them through the contact page for a quote by email.