What Is Shot Rock? Sizes, Uses and Shot Rock vs Riprap

What is shot rock? It is rock that has been blasted loose from a quarry face and sold more or less as it lands: no crushing, no screening, just a jumble of angular pieces from dust and chips up to big chunks. Builders use it when they need a lot of mass at a low cost, such as building up a low site or getting equipment across soft ground. This guide covers what shot rock looks like, where it works, where it does not, and how it differs from riprap.

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The short answer

What it is: unprocessed blasted quarry rock, also sold as blasted rock, quarry rock or rock fill.
Size: unsorted. Expect anything from fines to pieces a foot or more across, unless the quarry offers a rough size range.
Best uses: deep fill, lifting low sites, crossing soft or wet ground, construction entrances and embankments.
Not for: finished driving surfaces, fine leveling, under slabs or under pavers.

How shot rock is made

Quarries drill a pattern of holes into the rock face, load them with explosives and fire the shot. The face breaks into a pile of fractured rock. Most of that pile goes to the crusher to become sized products such as #57 stone, crusher run or screenings. Shot rock is the material sold before that step. Because the pieces come straight off a fracture, they are sharp and angular, which helps them lock together when placed.

What you get depends on the quarry. Granite, limestone, basalt and other rock all blast differently, and the same quarry can produce a finer or coarser pile depending on the blast. Some yards sell true run-of-quarry rock; others pick out oversize pieces or sell a rough range.

What shot rock is good for

Building up grade. When a site needs several feet of fill, big rock is a cheap way to add volume that will not settle like loose soil.
Bridging soft or wet ground. Large pieces can spread a load over mud where smaller stone would sink and pump. It is often pushed into a soft area until it stops moving, then capped.
Construction entrances and haul roads. A pad of large rock knocks mud off tires and holds up to heavy equipment for a season.
Embankments and rock buttresses. Its weight and interlock help hold a slope, under an engineer's design where needed.
Rough erosion work. Some quarries sell blasted rock for light erosion control, but structural bank protection usually calls for graded riprap.

Where shot rock is the wrong choice

As the top surface. The big, sharp pieces are rough on tires, boots and mowers. Plan to cap it.
Under slabs, footings or pavers. Those need a graded base that can be compacted to a smooth, even plane.
Thin layers. You cannot spread rock with foot-wide pieces two inches thick. Shot rock only makes sense where the layer is at least as thick as the largest stones.
Near buried pipes or liners. Large angular rock can damage pipe or fabric; bed and cover those with smaller stone first.

Shot rock vs riprap

The two look similar in a pile, and the same quarry may sell both, but they are bought for different jobs.

Sizing. Riprap is sorted into size classes. Highway agencies define classes by stone weight or size, and ASTM D6092 gives standard size designations for erosion-control stone. Shot rock is not sorted.
Quality checks. Riprap for a channel or shoreline is usually tested for durability. Shot rock may be fine rock, but nobody has proven it for that job.
Placement. Riprap goes down in a designed layer thickness, often over filter stone or fabric; see riprap sizes and weight. Shot rock is usually dumped and pushed as fill.
Cost. Because it skips processing, shot rock is often one of the cheaper stone products a quarry sells. Prices vary by region and haul distance, so get a quote.

If the plans call for a riprap class, buy riprap. If you just need bulk rock to fill or stabilize, shot rock may be the better value.

How to cap shot rock

A typical build over soft ground is a layer of shot rock, then a graded large stone such as #1 stone or a 2 to 3 inch base stone to fill the big voids, then a dense-graded stone with fines such as crusher run that compacts into a driving surface. Separation fabric between soft soil and the first rock layer helps keep mud from working up into the stone; our driveway fabric guide explains the types.

How much shot rock to order

Find the area in square feet and the thickness in feet. The layer should be at least as thick as the largest pieces.
Multiply to get cubic feet, then divide by 27 for cubic yards.
Ask the quarry how many tons per cubic yard their shot rock runs. A pile with lots of fines packs heavier than one with mostly large blocks.
Multiply yards by that density for tons, and add extra for rock that sinks into soft ground. On mud, that extra can be a lot.

Example: a 20 by 40 foot pad at 18 inches thick is 800 × 1.5, or 1,200 cubic feet, about 44 cubic yards. If the quarry says its rock runs 1.5 tons per yard, that is about 67 tons before any allowance for sinking. Treat that density as a placeholder until you have the quarry's figure.

Questions people ask

What is shot rock?

Shot rock is rock broken loose from a quarry face by blasting and sold without crushing or screening. It comes as an unsorted mix of angular pieces, from fines and small chips up to large chunks.

What size is shot rock?

There is no single size because it is not screened. Some quarries sell it as is, and others offer it sorted into rough ranges such as several inches to well over a foot. Ask the quarry for the largest piece you should expect.

What is shot rock used for?

Deep fill, lifting a low site, crossing soft or wet ground, construction entrances, embankments and some erosion work. It is a bulk fill, not a finished surface.

Is shot rock the same as riprap?

No. Riprap is stone sorted to a size class and usually tested for durability so it can armor a bank or channel. Shot rock is not graded, so it may not meet a riprap spec, though some quarries sell rough blasted rock for light erosion control.

Can you drive on shot rock?

Not comfortably. The big, sharp pieces make a rough, tire-punishing surface. Cap it with a graded stone such as a large base stone and then a layer with fines before regular traffic.

How much does shot rock weigh?

It depends on the rock type and how much fine material is mixed in. Solid stone is heavy, but the gaps in a pile lower the weight per yard. Get the quarry's figure; our riprap guide uses about 1.4 to 1.6 tons per cubic yard placed for graded riprap as a comparison.

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