#89 Crushed Stone in Maryland: Small, Angular and Carrying Its Own Fines

Push a hand into a pile of #89 crushed stone and it behaves nothing like the washed sizes stacked next to it in the yard. The chips run to about 3/8 inch at the top, they are sharp rather than water-worn, and a gray dust comes away on your glove because the grading carries fines all the way down. Squeeze a handful and it holds a shape for a second before it falls apart. That is the whole character of the material, and it is why it ends up in joints and under flagstone instead of in a drain.

• Size: about 3/8 inch down to fines.
• Grading: #89, carries some fines.
• Type: angular crushed stone.
• Approximate weight: about 2,800 lb per cubic yard, or 1.40 tons per cubic yard, using this site's own published figure for the small chip sizes.

Bedding and jointing flagstone, which is where most of these loads go

The typical order is the last stage of a patio or a walk. The base is in, compacted and checked for fall, and what is left is a thin leveling course to set stone into and something to fill the gaps between the pieces once they are down. Fines are an advantage in both of those jobs. They let the bed take the impression of an irregular flagstone underside, and they let a swept joint firm up instead of rattling loose every time someone crosses it.

The same behavior puts it into chip seal work, where an angular fine gradation binds into the surface treatment rather than sitting on top of it, and into concrete mixes that specify a small stone. What it is not built for is anything that has to keep water moving. Fines in the gradation are the reason this one belongs in confined hardscape areas and not in a drain run or behind a wall.

Mica-flecked Piedmont silt, Shore sand, and a joint that faces 30 inches of frost

Central Maryland soils weather out of schist and gneiss and often come out flaky with mica and full of rock fragments. They are silty, they hold water, and when they are saturated they turn soft and refuse to compact. Nothing in a joint fixes that, which is why the layer underneath has to be right before this material is opened. Patio work here belongs in the spring-to-late-autumn window, when the ground is firm enough to compact against.

On the Eastern Shore the soils are sandier and lighter, but flat, low ground and a high water table mean a patio can sit over ground that is still full a week after a nor'easter. A bedding course laid on saturated sand will find its own level and take the flagstone with it.

Frost sits at about 30 inches across most counties, 24 inches in Caroline, Dorchester and Queen Anne's, and 36 inches in Garrett. Joints that go into winter full and tight come through it far better than joints left half empty, because open gaps collect water and water is what lifts a stone.

Screeding the bed, setting the stone, sweeping the joints tight

• Screed the bedding course thin and even. It is a leveling layer of an inch or so, not a substitute for base, and thickening it over a low spot only moves the settlement to a later date.
• Set each piece, tap it down and check it against its neighbors as you go. Lifting a flagstone back out to correct it is easy while the bed is fresh and tedious once the surrounding stones are set.
• Sweep the joints in more than one pass. Fill, wet or vibrate lightly, then fill again. A joint always takes more on the second pass than you expect.
• Work a stiff broom diagonally across the joints so the material drops in rather than skating across the surface.
• Keep the last wheelbarrow-load back. Joints drop over the first few weeks and having the same stone on hand beats trying to match it later.

Fines or no fines: #89 crushed stone, #8 and stone dust

Two neighbors on the product list do similar work, and the difference is what is in the gradation rather than what is on the top size.

Pick this one when a joint has to hold and the surface is not doing drainage duty. Pick the clean stone when the point of the patio is that water goes through it.

The wall, the pond edge and the site entrance: three loads to price honestly

Square feet times depth in feet, divided by 27, gives cubic yards. Multiply by the tons-per-yard figure for tons. All four of these are worked examples, not real projects.

• Example, the job this page is actually for: a flagstone walk 34 feet long and 4.5 feet wide, or 153 square feet, on a 1.5 inch bedding course. 1.5 inches is 0.125 feet, so 153 x 0.125 = 19.1 cubic feet, divided by 27 = 0.71 cubic yards, about 1.0 ton before the joint sweep.
• Example, drainage backfill behind a 30 foot retaining wall, 12 inches wide and 3 feet deep: 30 x 1 x 3 = 90 cubic feet, divided by 27 = 3.33 cubic yards. That volume wants Drain Rock, which is washed specifically so the voids stay open under the weight of the soil above.
• Example, a pond or shoreline edge 45 feet long and 2.5 feet wide, or 112.5 square feet, at 4 inches: 112.5 x 0.3333 = 37.5 cubic feet, divided by 27 = 1.39 cubic yards. Stone this small will not stay at an edge that sees wave action or storm flow. A visible edge suits Large River Rock, and a tidal bank losing ground wants RipRap.
• Example, a construction entrance 40 feet by 12 feet, or 480 square feet, at 6 inches: 480 x 0.5 = 240 cubic feet, divided by 27 = 8.89 cubic yards. At about 1.45 tons per cubic yard for the coarse sizes, roughly 12.9 tons of #4 Crushed Stone. Small chips would simply be pushed into the mud by the first loaded truck.

Work the square footage, then run it through the gravel calculator if you want the conversion checked. Delivery is arranged at checkout by ZIP code, and the delivery page covers what the truck needs at the other end.