3/4" Crushed Stone: What It Locks Into, and What It Never Becomes

A pile of it does not slump. Push a shovel in on a hillside job where the ledge is a foot down and the face of the heap stands up at an angle a rounded stone could never hold. That is the first thing worth knowing about 3/4" crushed stone, because everything it does well follows from it.

Approximately 3/4 inch, angular, crushed from rock rather than worn by water. It interlocks under load and it passes water while doing so, which is a combination not many materials manage.

In the pile: flat faces, one size, nothing powdery at the bottom

The pieces are irregular and the faces are flat, with corners that catch on a glove. Sizes run close together, so there is nothing fine filling the spaces between them.

Kick the bottom of the pile and no dust comes off it. That matters more than it sounds. The gaps between the stones are permanent, because there is nothing small enough in the mix to migrate down and close them.

Under a plate compactor the layer tightens and the corners wedge. It does not turn into a sealed surface and it never will, and that is a feature in the places this stone belongs.

Set it beside #57 stone, drain rock and crusher run

Four materials that overlap, kept apart by what each one is asked to do.

If a drawing specifies #57, order #57, since the grading number is the point. If the trench is wide and nothing sits on it, the bigger washed stone moves more water per shovelful. If you want a surface that packs down hard and holds a crown, the fines in crusher run are what does that, and no amount of compaction will get this material there.

Under a garage pad, behind a wall, along a ditch line

Subbase under pads and footings. Compacted under a shed or garage slab, a footing, or a building pad, it carries the load and gives water sitting in the till somewhere to go instead of against the concrete.

Retaining wall backfill. A vertical chimney of it against the back of the wall lets water reach the drain at the bottom rather than building pressure behind the blocks through a wet spring.

Ditch and culvert drainage. Along a ditch line that runs hard for a few weeks in April and sits dry the rest of the year, it holds its form where a finer material would wash.

Under a camp road build. As the compacted upper layer on a road section that has to stay firm on ground holding water, with a coarser material below where the build calls for it.

A rock garden bed and a culvert outlet are somebody else's stone

Two of the jobs people ask for it by name.

A decorative rock garden bed. Nothing structurally wrong with it, but crushed granite grays down, holds leaf litter in the gaps and looks like a construction material because it is one. Use this instead: river rock for a bed meant to be looked at, or pea stone for a finer texture.

A culvert outlet. Where spring runoff comes out of a pipe with force behind it, a 3/4 inch stone is small enough for the water to carry away, and a season or two later it is in a bar twenty feet downstream. Use this instead: RipRap, sized to what you have watched that outlet do in a hard thaw.

Four inches under a pad, a foot behind a wall

Compact in lifts of 4 inches, not in one deep pour. Fabric goes under it any time the layer sits on till or silt, because a clean stone with no fines has no defense against soil pushing up into it from below.

Where ledge is close to grade there is often no room to dig the full depth. Build up rather than down, and accept that the finished grade rises.

Tons for a 12 by 22 garage pad and 36 feet of ditch lining

Two hypothetical jobs. This material sits in the #57 and 3/4 inch family on the weights this site publishes, about 2,800 lb per cubic yard, near enough to 1.40 tons per cubic yard.

Subbase under a 12 ft by 22 ft garage pad, 6 inches

• 12 x 22 = 264 sq ft
• 264 x 6 / 12 = 132 cu ft
• 132 / 27 = 4.89 cu yd
• 4.89 x 1.40 = 6.85 tons, so order 7

Ditch lining, 36 ft long, 4 ft of wetted width, 6 inches

• 36 x 4 = 144 sq ft
• 144 x 6 / 12 = 72 cu ft
• 72 / 27 = 2.67 cu yd
• 2.67 x 1.40 = 3.74 tons, so order 4

A ditch is a trough rather than a flat rectangle, so measure the width up the sides of it, not across the top. Anything with a curve or a slope in it goes through the stone calculator.

Getting a load onto a hillside lot without moving it twice

Clean stone rolls when it lands. On a slope it keeps rolling. Pick a flat drop spot the machine can reach in one pass, as close to the work as the ground allows, and keep it off finished lawn.

A plate compactor handles the depths above on a pad. A hand tamper will do a wall chimney or a short ditch section, though the layer needs less work than a material with fines in it does. Set the quantity and a delivery date on this page. Delivery is arranged at checkout by ZIP code, and the truck wants firm ground and room to back.