#67 Stone: the Smaller Open Grade, and When to Pick It

Half the people who land on #67 Stone arrived here meaning to buy the number above it, and the other half were sent by a drawing that specified one number and nothing else. On a Wisconsin lot where the ground stays saturated for weeks after the thaw, the difference between the two is worth a minute of reading, because it changes how a trench drains, how a pipe beds and how a pour finishes.

The grading is #67, the size runs 1/4 inch to 3/4 inch, and the type is angular crushed stone.

Is this the same rock as #57 Stone, only smaller?

Same rock, different screen, and the screen is the whole product.

• The range starts finer. Where the larger grade begins around 3/4 inch, this one carries pieces down to a quarter inch, so the mix packs closer together.
• Closer packing means smaller voids. It still drains freely, but it holds a little less water per yard and sheds silt less easily.
• It beds better around pipe and fittings, because smaller pieces settle into the shape of what they surround instead of bridging across it.
• It finishes a concrete pour more smoothly, which is why decorative and architectural mixes call for it.
• It looks tidier spread as a visible cover, with fewer oversized pieces standing proud.

If a drawing, a mix design or an inspector names a number, order that number. These are separate graded products, not interchangeable sizes.

What does a 1/4 to 3/4 inch grade do on ground that will not drain?

It gives water a route that the subgrade cannot give it.

• In reddish lake clay around Green Bay, Lake Winnebago and the Fox Valley, water cannot soak down at all while the subsoil is still frozen, so it sits. An open stone layer holds it somewhere harmless and moves it to an outlet.
• On Driftless silt loam, runoff comes fast off the ridge and then vanishes into cracks, sinkholes and springs. Trench routes there follow where the water actually goes.
• On Central Sands outwash the ground already drains. The stone is there for bearing and for keeping sand out of a pipe zone.
• In Northwoods till the rises are stony and sandy and the hollows are peat and muck. Put the drainage where the hollows are.
• Under a turnaround or a low pad, an open lift gives meltwater somewhere to sit below the surface instead of standing on it.

Which jobs on my lot need fines instead of this?

Plenty of them, and buying the wrong one is an expensive week.

• A driving surface. Open stone rolls under a tire. The surfacing you want is Driveway Gravel.
• A compacted base. Nothing here binds, so the layer will not tighten. That is 3/4" Traffic Bond.
• A paver bedding course. It needs a fine, screedable material, so use Screenings.
• Deep correction of soft ground under a lane, which wants a coarser, heavier stone than this.

Use this grade for the part of the build that is meant to carry water, and let a different product carry the load.

How do I keep the voids open in a trench full of silt?

A drain fails when the gaps between the pieces fill in, and Wisconsin soils are good at filling them.

• Line the trench with separation fabric and lap it over the top of the stone before backfilling.
• Keep the stone clear of topsoil at the finished grade, or the surface will wash silt straight into the top of the drain.
• Give the run a continuous fall to a daylight outlet, a sump or a ditch. Level stone in a level trench just stores water.
• Bed pipe fully, underneath as well as around, so the line is supported evenly along its length rather than on a few high points.
• Behind a wall, carry the stone column down to a drain line so water leaves the back of the wall rather than pushing on it.

How much do three jobs on one wet lot actually take?

Square feet times depth in inches divided by 12, divided by 27 for cubic yards. This site publishes roughly 2,800 lb per cubic yard for the #57, #67 and 3/4 inch crushed stone family, or 1.40 tons per yard, so multiply the yardage by 1.4. Hypothetical examples:

• Turnaround pad, 18 ft by 18 ft, open lift at 5 inches: 324 sq ft x 0.417 = 135 cubic feet. 135 divided by 27 = 5.0 cubic yards, or about 7.0 tons.
• Foundation drain, a trench 56 ft long and 1.5 ft wide carrying 2.5 ft of stone: 56 x 1.5 x 2.5 = 210 cubic feet. 210 divided by 27 = 7.8 cubic yards, or about 10.9 tons.
• Low spot in the yard opened out as an infiltration pocket, 10 ft by 12 ft at 12 inches: 120 sq ft x 1 = 120 cubic feet. 120 divided by 27 = 4.4 cubic yards, or about 6.2 tons.

Open-graded stone barely settles, so what you order is close to what you see. Round trench figures up, because a short load on an open trench means leaving it open overnight. The Stone Calculator will confirm the arithmetic.

Choose a quantity and a delivery date on this page. Delivery is arranged at checkout by ZIP code, so have a firm drop picked out that a loaded truck can reach and leave without crossing soft ground.