#4 Crushed Stone: the Coarse Lift Under Wisconsin Mud

Tip a load of this out and it does not look like gravel at all. The pieces run about 3/4 inch to 1-1/2 inches, every face is broken and sharp, and the gaps between them are wide enough to lose a glove in. Pick one up and it has weight to it. That combination, big angular pieces and deliberate empty space, is the whole design of #4 Crushed Stone, and it explains why it goes at the bottom of a build rather than anywhere near the top.

The March problem this stone is bought to end

Every spring the same phone call goes out on rural lanes across the state.

• The top of the ground thaws while the subsoil beneath is still frozen solid, so meltwater has nowhere to drain.
• Saturated subgrade has almost no bearing strength, and one loaded axle presses straight through a thin gravel layer.
• The ruts fill, freeze again overnight, and the surface breaks up further with each cycle.
• A finer material dumped on top simply sinks into the soup and disappears.

Large open stone works because it does two jobs at once. The pieces interlock and bridge over soft ground, so weight is spread rather than concentrated, and the voids between them carry water out sideways instead of trapping it under the traffic surface.

How it behaves on red clay, muck hollows and Driftless grade

• Red clay on the Lake Superior plain and the tight lake clays around Green Bay and the Fox Valley are the classic use. Stone laid straight on saturated clay gets pushed into it, so the layer has to be thick enough and separated from the clay to stay put.
• Peat and muck hollows through the Northwoods and the Chippewa Valley stay soft longest. These are the spots that swallow two loads of anything finer.
• Central Sands outwash rarely needs a lift this heavy, except in the low ground of the old lake bed.
• On Driftless slopes and stream banks, the weight of the individual pieces is the point. Angular rock this size stays where it is put when runoff comes off a ridge in a summer storm.
• In a ditch or a channel, the same mass resists scouring where a lighter material would wash out by July.

Strip, separate, dump and cap

• Cut out the failed material and the sod. Building over a rutted, organic mess only buries the problem.
• Lay separation fabric on clay and on anything with peat in it. Without it, the stone migrates down and the clay migrates up.
• Dump and spread in one lift rather than thin layers. This size does not compact into anything, it locks together, so the pieces need room to nest.
• Track it in with a machine bucket or a loaded axle rather than a plate compactor. The aim is to seat the pieces, not to crush them.
• Cap it. The open surface is unpleasant to walk on and will swallow small items, so a lane gets 3/4" Traffic Bond over the top, then a surfacing course.

What it asks for after the first spring

• Walk the lane once frost is out and look for spots where the cap has thinned and the coarse stone is showing through. Top the cap, not the base.
• Check the ditch line and any culvert ends. The lift only works while the water it collects has somewhere to leave.
• On a slope or a ditch, look for pieces that have shifted downhill after the melt and reset them before the next storm.
• Do not blade it. A grader blade on an open stone layer drags the whole surface out of position.

Tons for an RV pad, a long lane and a path across a wet swale

Square feet times depth in inches divided by 12, then divided by 27 for cubic yards. This site publishes about 2,900 lb per cubic yard for the #4 stone and railroad ballast family, or 1.45 tons per yard, so multiply the yardage by 1.45. Three hypothetical jobs:

• RV and boat parking pad, 12 ft by 35 ft at 8 inches: 420 sq ft x 0.667 = 280 cubic feet. 280 divided by 27 = 10.4 cubic yards, or about 15.0 tons.
• Rural lane rebuild, 10 ft wide by 300 ft long at 6 inches: 3,000 sq ft x 0.5 = 1,500 cubic feet. 1,500 divided by 27 = 55.6 cubic yards, or about 80.6 tons.
• Garden path crossing a wet swale, a drainage lift 3 ft wide by 45 ft long at 6 inches: 135 sq ft x 0.5 = 67.5 cubic feet. 67.5 divided by 27 = 2.5 cubic yards, or about 3.6 tons.

The path figure covers the lift only. The walking surface on top is a separate, finer order, and Walkway Gravel or 3/8" Crushed Stone is the material for it. Check any of these numbers in the Stone Calculator.

Pick your tonnage and a date on this page. Delivery gets arranged at checkout from your ZIP code, and a load of stone this coarse wants a straight, firm run in and room for the box to come up.