#4 Crushed Stone: The Open Grade for Soft New York Ground

Stand over a fresh pile of #4 crushed stone on a North Country site in early May and the material argues its own case. You pick the pieces up one at a time rather than by the shovelful. They are freshly broken, sharp at every corner, and stacked loose enough that you can see light down into the pile. Rain falls on a heap of this stone and disappears instead of running off it. That combination, big angular pieces with large clear gaps between them, is what gets ordered when the ground underneath a job will not stay firm.

One thing to settle before ordering. Ask for it by grade number, not by a measurement. NYSDOT's own size 4 in its stone table is a far larger rock than the #4 grade sold here, so an inch figure quoted over the phone in a New York yard can mean two very different materials. The grade number is unambiguous.

Why #4 crushed stone gets ordered in April, not August

New York's base season opens with the thaw and closes when the ground freezes. That window is the whole story for this material, because the reason to buy it is usually a subgrade that has gone soft, and subgrades go soft at the two ends of the season rather than the middle.

In spring the frost comes out of the ground from the top down while the layer below is still locked. Meltwater has nowhere to go, so it sits in the thawed zone and turns till, silt and clay into something an excavator sinks into. On Tug Hill and in the snow belts east of the lakes, a deep pack can keep that going for weeks. Late in the year, after the autumn rains, the same flat clay ground in the St. Lawrence and Champlain plains holds water with no growing season left to dry it out.

Those are the two stretches when a job stops for want of a firm layer to work off, and they are when this grade earns its keep. In July on the sandy outwash of Long Island, it is rarely the answer to anything, because the ground there drains on its own.

Getting a soft spring subgrade ready to take stone

Do not mix the stone into the mud. That is the mistake that wastes a load. Big open stone pressed into saturated fines fills its own voids with the fines and becomes a heavy, wet layer that does nothing.

Strip the softest material off first and get down to something that at least holds a boot print rather than swallowing it. Then lay a separation fabric across the whole area, lapped at the joins and run up the sides of the excavation. On the silt and clay valley floors of the Hudson and Mohawk, and on flat lake-plain ground, that fabric is not optional if you want the layer working in five years.

Place the stone in one lift onto the fabric and push it out with a bucket rather than driving on it until it is covered. Then bring the finer material over the top. On a job that has to carry traffic, the finer material is a compacting base such as Item 4 or crusher run, because this grade is never the driving surface.

Under a pole barn floor, under a drive and under a wet walkway

Three jobs cover most of what leaves here.

A pole barn or equipment pad on wet ground gets this grade as the bottom layer, thick enough to bridge the soft spots, with a compacted base and then a floor or a surface over it. The open voids give meltwater somewhere to go instead of pumping up under the pad every spring.

A single-car gravel driveway on a hillside site uses it the same way, as the bottom course under the base and surface. It is also the standard material for a construction entrance at a road connection, where stone big enough to shake mud off a tire is the point.

A flagstone walkway across ground that stays wet gets a thinner version of the same sandwich: this stone as a drainage course, fabric under it, then a compacted base and a bedding layer of stone dust above. On dry ground the drainage course is unnecessary and the base alone is plenty.

Gabion baskets and slope or ditch work round out the list, though once stone has to hold a bank against moving water, RipRap rather than this grade is the material.

Stone for a 30 by 40 pole barn pad and a 90 foot drive

Hypothetical layouts, with the arithmetic written out.

Pole barn pad, 30 by 40 ft, 6 in of open stone

• 30 x 40 = 1,200 sq ft
• 1,200 x 6 / 12 = 600 cu ft
• 600 / 27 = 22.22 cu yd

Single-car drive, 10 by 90 ft, 6 in

• 10 x 90 = 900 sq ft
• 900 x 6 / 12 = 450 cu ft
• 450 / 27 = 16.67 cu yd

Flagstone walk, 4 by 26 ft, 4 in

• 4 x 26 = 104 sq ft
• 104 x 4 / 12 = 34.7 cu ft
• 34.7 / 27 = 1.28 cu yd

Together that is 40.17 cubic yards. This site publishes roughly 2,900 pounds per cubic yard for the #4 and ballast family, about 1.45 tons per yard, so the three areas come to near 58.2 tons. Order 58 and allow for the layer being pushed into soft ground in places. Take the weight as approximate, and run the same figures through the stone calculator if your areas are more awkward than rectangles.

What the first freeze-up tells you

Watch the layer through its first winter. Where the fabric was laid properly and the cover above it is thick enough, nothing much happens: water moves down, frost does its work in a layer with room to move, and spring arrives without a heave. Where the stone went straight onto soft ground, the first thaw shows it as a dip, usually in the wheel track or under the corner that carries the most weight.

The fix at that point is not more of the same stone. It is to open the spot up, get fabric underneath, and rebuild. Which is why the hour spent laying fabric in April is the hour that saves the most work later.

To order, set a tonnage and a delivery date on the product page. Delivery is arranged from your ZIP code at checkout, and a loaded truck needs a firm, clear place to tip, which on a spring site is worth checking the morning of rather than the week before.