#8 Crushed Stone in Maryland: The Clean Small Size for Joints and Bedding

A good share of the #8 crushed stone ordered onto Maryland lots is bought to undo something. A permeable patio was bedded on sand, or a downspout trench was packed with a material carrying dust in it, and by the third August thunderstorm the water is running sideways across the Piedmont clay underneath instead of down through the surface it was meant to pass through. Small clean stone is the correction, because the space between the pieces is the whole point of it.

That weight is this site's own published figure for the small chip sizes, and it is an approximation rather than a certified density.

Standing water on a permeable patio three storms after it was laid

The failure is almost always the same. A surface built to let water through has one layer in it that does not, and that layer decides the whole thing. Fine material in the setting course, or fines washed down into it from a dusty joint, fills the gaps between pieces and turns a drainage path into a shallow pan. Clean stone at 3/32 to 3/8 inch is sized so the voids stay open under weight, which is why it is specified for the setting layer beneath permeable pavers and for the joints between them.

The same reasoning runs through the other jobs on the list. Pipe laid on a bare trench bottom bears on the high spots and bridges the low ones. Set on and covered with this stone, it is supported evenly and water still moves past it. Concrete batches that call for a smaller coarse aggregate use it for much the same reason the joints do: consistent piece size, nothing fine riding along.

Open voids over Piedmont clay, over Shore sand and through 30 inches of frost

Central Maryland sits on loam and clay loam weathered from hard crystalline rock, and rolling ground sheds a thunderstorm quickly toward the stream valleys. The water arrives fast, which suits a surface that can take it in fast. What clay does badly is accept the water once it is through, so a permeable build on Piedmont ground needs somewhere for the water to go at the bottom of the layers, not just a route into them.

The Eastern Shore reverses the problem. Sandy Coastal Plain ground takes water readily, but flat, low land and a high water table mean the ground below can already be full after a nor'easter. Keep the clean stone layer above wet ground rather than sitting in it.

Frost runs to about 30 inches across most of the state, 24 inches in several Eastern Shore counties and 36 inches in Garrett County. Open-graded stone holds very little water itself, so it heaves far less than a saturated fine material, and that is half the reason it is the bedding of choice for hardscape that has to come through February looking the way it did in October.

One check before a large permeable area goes in. Within 1,000 feet of tidal water, Critical Area rules limit how much of a lot can be covered, and gravel and stone surfaces count toward that figure.

Getting #8 crushed stone from the driveway pile into an open joint

Keep the stone off soil from the moment it lands. Ask for the drop on a tarp, on plywood or on a clean part of the drive, because a pile tipped on a lawn collects exactly the mud the material was chosen to avoid. Then work in this order:

• Finish and check the layers underneath first. The setting course is a thin leveling layer, not a structural one, and it cannot correct a base that is out of level.
• Screed the setting course to a consistent thickness, commonly around 2 inches, and resist the urge to thicken it where the base dips.
• Set the units, then sweep the same stone into the joints in passes, filling, vibrating and filling again until the joints stop taking material.
• Around pipe, bed below the pipe first, then place and firm in lifts on either side so the pipe is supported rather than pushed off line.
• Rinse loose dust off the surface at the end. Anything left on top washes into the joints in the first rain.

What the joints do over a Maryland winter, and the spring sweep

Open joints lose a little material in the first season, and that is normal rather than a fault. Freeze and thaw work the top of the joint loose, summer downpours carry a small amount out over the edge, and foot traffic grinds a fraction of it down. The upkeep is a top-up sweep once a year, and the tell that the job needs it is water sitting on the surface for more than a few minutes after rain.

Two things are worth watching for. Leaf litter and grass clippings rotting on a permeable surface will plug it sooner than anything else will, so a blow-off in late autumn saves a lot of work later. And check where the water goes once it is through the layers. A drain outlet that has silted up will back water into the stone from underneath, which looks like a surface failure and is not one.

Tons for a bed-surround apron, a play area sub-layer and a boat pad

Square feet times depth in feet, divided by 27, gives cubic yards. Multiply by 1.40 for tons at the approximate weight above. Each of these is a worked example rather than a real project.

• Example, paths running between raised vegetable beds. Two runs at 24 feet by 3 feet is 144 square feet, plus a cross path 10 feet by 3 feet at 30 square feet, so 174 square feet. At 3 inches, which is 0.25 feet: 174 x 0.25 = 43.5 cubic feet, divided by 27 = 1.61 cubic yards, about 2.3 tons. Clean stone drains here and keeps mud off boots between the frames.
• Example, a play area 18 feet by 22 feet, or 396 square feet, taking a 4 inch drainage layer underneath: 396 x 0.3333 = 132 cubic feet, divided by 27 = 4.89 cubic yards, about 6.8 tons. The layer children actually land on is a separate question, and angular chips are not it. 3/8" Natural Pea Gravel is rounded, or Shredded Mulch where a softer cover suits the space.
• Example, a boat or RV pad 11 feet by 28 feet, or 308 square feet, with a 2 inch setting course: 308 x 0.1667 = 51.3 cubic feet, divided by 27 = 1.90 cubic yards, about 2.7 tons. That figure only applies to a permeable build where the layers below are open-graded stone as well. A pad meant to carry a trailer on an ordinary base wants CR-6 compacted in lifts, and this stone has no business in it.

Those three come to roughly 11.8 tons together. Put the square footage through the paver base calculator if you would rather have the tool handle the conversion.

Measure, pick a depth, then set a quantity and a delivery date on this page. If the joints and the bedding are going on one order and you want both figures checked together, send the dimensions through contact first.