#89 Crushed Stone: The Small Angular Stone That Packs

Stand three shovels up in three piles at the start of a hardscape job in the Lakes Region and two of them will look identical until you pick the stone up. Getting that choice wrong is what has a flagstone landing rocking by the second winter.

#89 crushed stone is the one with fines in it. About 3/8 inch down to dust, angular, graded to the #89 band. The fines are not contamination. They are what lets the layer lock up tight in a confined space and stay where it was compacted.

Three piles that look alike: #89 crushed stone, stone dust and #8

The differences show up in the hand, not the eye.

Stone dust is the New England default under flatwork and it is still the right answer for a tight flagstone bed on a well-drained base. #89 is what to reach for when you want a little more drainage through the setting course and a surface that is a fraction more forgiving to screed.

The one to be careful about is #8. Same size, opposite behavior. A clean stone in a paver bed will not hold a screed line, and a stone with fines in a drain trench will plug within a few seasons.

Where the fines earn their place: joints, setting beds and a chip seal

Joint fill between pavers or flagstone, worked in with a broom until the joints stop taking more. The angular pieces and the dust wedge together and the units stop shifting against each other.

The setting course under a paver apron or a flagstone landing, spread and screeded to a constant inch, then compacted in place.

A path base under stone walkways, where the layer has to be flat and stay flat rather than pass water.

Chip and seal surfacing, and as the smaller coarse aggregate in a concrete mix where the gradation calls for it.

What all four share: the layer is confined. Something sits on top of it or beside it. Loose on open ground, a fines-bearing stone turns to a dusty crust in July and a soft patch in April.

Send a culvert outlet and a rock garden bed somewhere else

Two jobs people ask this stone to do that it will not.

A culvert outlet or a ditch line. Moving water sorts a graded stone in one spring. The fines wash out first, then the small stuff, and what is left sits in a bar downstream of where you put it. Use this instead: RipRap where the water has force behind it, or #4 crushed stone in a quieter ditch that only runs hard for a few weeks.

A rock garden or decorative stone bed. The dust in it grays over, holds moisture against crowns, and gives weed seed something to sit in. Use this instead: pea stone for a fine look, or river rock where the bed is meant to be the feature.

One inch under a shed apron, never four

The setting course is an inch. Not two, not three. A thick bed of any small material compresses unevenly under load, and the pavers telegraph every soft spot the following spring.

What carries the weight is the layer below: 4 to 6 inches of compacted crushed gravel under a walk, more under anything that takes a wheel. On dense till near ledge, dig the base deep enough that water is not sitting under the pavers when the frost comes out.

Sequence on a shed apron: excavate, compact the subgrade, base in two lifts, screed the #89 to an inch, set the units, sweep the joints, compact, then sweep again once it has settled.

Tons for a 10 by 12 shed apron and an L-shaped landing

Hypothetical jobs, setting course only. This size sits in the 3/8 inch chip family on this site's published figures, about 2,800 lb per cubic yard, near enough to 1.40 tons per yard. That figure is approximate for a stone that carries fines, so round up rather than shaving it.

Shed apron, 10 ft by 12 ft, 1 inch bedding

• 10 x 12 = 120 sq ft
• 120 x 1 / 12 = 10 cu ft
• 10 / 27 = 0.37 cu yd
• 0.37 x 1.40 = 0.52 tons

L-shaped landing, 1 inch bedding

Break an odd shape into rectangles you can measure with a tape and add them. Here, an 8 ft by 5 ft rectangle with a 4 ft by 6 ft leg off it:

• 8 x 5 = 40 sq ft, plus 4 x 6 = 24 sq ft, total 64 sq ft
• 64 x 1 / 12 = 5.3 cu ft
• 5.3 / 27 = 0.20 cu yd
• 0.20 x 1.40 = 0.28 tons

Path base under a 60 ft stone walk, 3 ft wide, 2 inches

• 60 x 3 = 180 sq ft
• 180 x 2 / 12 = 30 cu ft
• 30 / 27 = 1.11 cu yd
• 1.11 x 1.40 = 1.55 tons

Add a quarter ton for joints and for the topping-up that follows the first rain. Anything with a curve in it goes through the stone calculator.

Picking a day and a drop spot for a stone that packs

A fines-bearing material does not want to sit in the rain on bare ground before it goes down. Wet, it screeds badly and drags under a straightedge; on grass, the fines stay behind after the pile is gone.

Drop it on a tarp or a hard surface within a wheelbarrow run of the work, and pick a stretch of dry weather rather than a date that suits the calendar. Choose the quantity and a delivery date on this page, with delivery arranged at checkout by ZIP code. If your area is a curve or a triangle, send the measurements through the contact page and work the volume out before you commit to a number.