3/8" Crushed Stone: the Finish Layer for Missouri Drives and Trenches

Chert comes up with every other shovelful on an Ozark lot, and a spade goes into Bootheel silt like it is going into a sack of flour. Between those two there is loess on the river bluffs that gullies the moment it is left bare, and claypan under the northern prairies that holds water on top instead of letting it through. A finish layer has to suit the ground it is sitting on, and that is really the only question worth asking about 3/8" crushed stone: what is underneath it, and is that firm enough to hold a small stone up.

3/8" crushed stone set against walkway gravel, screenings and chips

Four materials on this site land within a whisker of each other in size, and the differences are all in behavior.

Walkway Gravel is the path product. If what you are building is a garden route people walk on, start there rather than here.

Screenings go finer, a quarter inch down through dust, and they set up hard enough to bed a paver. That firmness is the point of them and it is also why they wash out of anything exposed to running water.

#8 Crushed Stone is washed, so it stays loose and open on purpose, and belongs around pipe and in permeable paver work rather than on a surface.

This grade sits in the middle: angular, roughly three eighths of an inch, with enough bite in the faces to knit down under a roller and tidy enough to leave exposed. It closes the gaps in a coarser layer below it and gives a drive or a bed a finished top without going as fine as a screening.

Topping a chert lane where the base underneath is already sound

The lane that suits this material is one that was built properly and has simply gone tired. Ruts starting to show, the surface loose in places, the crown flattening out, but a firm course still under it when you scrape a boot across.

Grade the lane first and pull the material back off the shoulders into the middle so the crown comes back. Then spread a thin, even layer of this stone and compact it. The small angular pieces work down into the gaps in the larger stone below and the surface tightens up. A lane treated that way sheds a thunderstorm instead of holding it in ruts.

Where it does not help is a lane that has failed from below. If the ruts come back within weeks, or the surface pumps water when a truck goes over it, the base has gone and no amount of finish stone will bring it back. That is a rebuild from the base up, not a top dressing.

Bedding a line in a trench dug through Kansas City clay

Utility bedding is the other job this size does well, and it is not the same work as a French drain.

Bedding is about support. A conduit or a water line laid straight on a clay trench bottom rests on whatever lumps the bucket left, and that is where it fails. Four inches of this stone raked level gives the line continuous bearing, and the even piece size lets it settle into place around bends and fittings without leaving voids.

On clay that shrinks in a dry August and swells again in a wet spring, that layer also takes some of the movement out of the ground before it reaches the pipe. Bring the stone up around the haunches of the line rather than just underneath, and use the shoulder of a rake rather than a boot to work it in. Whether the trench also needs to drain is a separate question with a separate answer, and that one goes to Drain Rock.

A ditch line and a low corner will both swallow it

Two of the jobs that come up most often are jobs to spend the money elsewhere on.

Lining a culvert outlet or a ditch that runs after a thunderstorm is not work for a small stone. An Ozark hollow emptying into a ditch moves a stone this size like sand, and the lining ends up downstream in the first real storm. Armor of that kind wants RipRap sized against the flow, keyed in at the toe.

A low corner of a yard that ponds every spring will take a startling volume of stone and still be a low corner, because nothing has changed about the level. Raise it with Fill Dirt in compacted lifts and cap it, and keep stone for the places water is meant to travel through.

How thin a finish layer can go before the base shows through

Depth here is about coverage rather than strength, because the layer underneath is doing the load carrying.

An inch to an inch and a half is enough as a top dressing on a drive that already has a base, measured after rolling. Thicker than two inches and you have a loose layer that a tire can push around rather than a finish that knits into what is below.

In a bed or around a tree ring, two inches covers the ground properly. Anything under that and the fabric or the soil grins through the first time somebody walks across it.

In a trench, three to four inches under a line is the usual figure, brought up around the sides.

Tons for a 70 foot drive top-up and 35 feet of trench bedding

Two hypothetical jobs.

A single-car drive 70 feet long and 10 feet wide, top dressed at an inch and a half: 70 x 10 is 700 square feet, and an inch and a half is 0.125 feet, so 700 x 0.125 gives 87.5 cubic feet. Divide by 27 and that is 3.24 cubic yards. This site publishes about 2,800 lb per cubic yard for the 3/8 inch chip family, roughly 1.40 tons to the yard and approximate, so 3.24 x 1.40 comes out near 4.5 tons.

A 35 foot trench 18 inches wide with 8 inches of bedding: 35 x 1.5 x 0.667 is 35 cubic feet, 1.3 cubic yards, about 1.8 tons.

The stone calculator will run other shapes with depth guides and a five percent allowance for uneven ground that is on by default.

Where a fine stone should land when the yard is still soft

Spring is the wettest stretch here and it is also when most lane work gets ordered, which is a combination worth thinking about before the truck rolls in.

A loaded tandem on a soft yard leaves ruts you will be fixing afterwards, so pick a drop spot with a firm approach even if it means a longer wheelbarrow run. On a long lane, ask about splitting the drop into two heaps along the route rather than one at the end, since spreading downhill is far easier than carting uphill. Missouri Rock Supply arranges delivery at checkout by ZIP code and the truck needs clear access to somewhere it can tip.

When the tonnage looks right, set an amount and a delivery date on this page, or raise a tight approach through the contact page first.