3/4" Crushed Stone: Getting the Layer In Before the Ground Locks Up

There is a stretch from about late May to late October when Colorado ground will take the work. Before that the melt is still coming out of the subgrade and nothing compacts; after it, frost is in the top of the profile and a layer placed on frozen clay will settle out of true in spring. 3/4" crushed stone is the material most of that season's drainage and pad work gets built from, and the reason to plan the order around the calendar is that the stone is the easy part.

Sized at 3/4 inch and angular, which is the whole specification

Size approximately 3/4 inch. Type angular crushed stone. That is the spec, and it is short because the behavior follows directly from it.

Angular pieces at one nominal size interlock when compacted and hold that arrangement under load, which is what makes the layer stable rather than merely thick. Because the pieces are all roughly the same size, the spaces between them stay open, so water moves through the layer instead of collecting on top of it. Those two properties, structure and open voids in the same material, are why one stone ends up under driveways, behind walls and in drain trenches.

Where 3/4" crushed stone sits next to the stone either side of it

The catalogue holds three products that overlap with this one, and buyers mix them up constantly.

The short version: base and surfacing want the material with fines, enclosed drainage wants the washed material, and this one covers the ground in between, where a layer has to support something and drain at the same time.

A turnaround that carries a truck and a drain that carries the melt

Under a pad or a slab. Place it over a prepared subgrade and compact it in lifts before the concrete or the surface course goes on. The layer gives the slab a drained cushion, which matters where clay holds water within reach of the underside.

On a driveway on grade. Angular stone holds on a slope in a way rounded material does not, which is worth knowing on foothill drives where every storm otherwise moves gravel to the bottom.

Behind a retaining wall. A vertical zone of open stone against the back of the wall gives water somewhere to go instead of building pressure against the block.

In a French drain. Bed and surround perforated pipe with it and wrap the trench in filter fabric. Fines from the surrounding clay are the only thing that will stop it working.

Two places it is the wrong answer on a Colorado property

A low spot or a yard regrade is an earthwork job, not a stone job. Bring the grade up with Fill Dirt, compact it in lifts, and finish with Top Soil if anything is going to grow there. Filling a depression with clean stone gives you an expensive pit that collects silt.

The second is a bare decorative bed with nothing draining through it. Angular gray stone underfoot is unpleasant and it looks like what it is, construction material. Beds want River Rock.

Six tons for a 20 by 24 turnaround, seven for 60 feet of drain

Two hypothetical jobs, worked at this site's published 2,800 lb per cubic yard, which is 1.40 tons per cubic yard, and checked twice.

Turnaround pad, 20 by 24 ft, 3 inch layer over a compacted base. 480 square feet. 480 x 3 / 12 = 120 cubic feet. 120 / 27 = 4.44 cubic yards. At 1.40, that is 6.2 tons.

French drain, 60 ft long, 18 inches wide, 18 inches deep. 1.5 x 1.5 x 60 = 135 cubic feet. 135 / 27 = 5.0 cubic yards, or 7.0 tons. A 4 inch perforated pipe running the length takes up about 5 cubic feet of that, which is 0.19 cubic yards, so 4.8 cubic yards and 6.7 tons is the closer figure.

Round up rather than down on a trench. Running out with 10 feet of open excavation left is the one mistake that costs a weekend. The stone calculator handles up to five areas and adds 5 percent by default for exactly this.

Booking a load into the dry end of the season

Order once the excavation or the subgrade is ready, not before, because a stone pile sitting through two weeks of weather collects the fines you have just gone to the trouble of avoiding. Delivery is arranged at checkout by ZIP code and the truck needs clear access to a spot it can tip, so think about where a loaded truck turns on your property before you pick a date. Quantities and dates are set on this page; layer questions go to Colorado Rock Supply through the contact page.