57 Stone vs. Crusher Run: Which Base Stone Goes Where?

If you are ordering stone for a driveway, a patio base, a wall, or a drain, you will run into the 57 stone vs crusher run question fast. They look similar in the pile, they come from the same quarry, and they are priced close enough that cost will not make the decision for you. But they do opposite jobs, and using the wrong one is a mistake you usually find out about a year or two later.

Here is the short answer. Crusher run is a dense-graded stone with fines in it, and it compacts into a hard, tight layer. It is the default base under driveways, paver patios, and anywhere the ground needs to stay put. 57 stone is clean, open-graded, and drains freely. It goes where water needs to move: French drains, behind retaining walls, as a capillary break under basement and garage floors, and as a leveling pad. The rest of this article explains why, what the stone is called in Pennsylvania, and where people get it wrong.

What “Gradation” Means and Why It Decides Everything

Gradation is just the mix of particle sizes in a load of stone. That one property decides whether the stone locks up or drains.

Crusher run, also called dense-graded aggregate, has everything from pieces up to about 2 inches down to stone dust. When you compact it, the small particles fill the gaps between the big ones, the dust packs into what is left, and you end up with a layer that has very few voids. Walk on a properly compacted crusher run base and it feels like pavement.

57 stone is the opposite. It is screened to a narrow size range, roughly half an inch to an inch, and the fines are washed out. Every piece is about the same size, so they cannot nest into each other. Even after a plate compactor goes over it, there is open space between the stones, and that space is what lets water pass through.

So when someone says a stone is “compactable,” they mean it has enough fines to lock together. 57 stone will settle and tighten a little under a compactor, but it never truly locks. It stays loose by design.

57 Stone vs. Crusher Run: The Stability and Drainage Trade-Off

You generally cannot have both in one material. Stone that compacts tight holds water. Stone that drains freely does not lock up.

Crusher run, once compacted, is dense enough that water moves through it slowly. That is fine as long as the layer is pitched to shed water and there is somewhere for it to go. It is a problem when the base sits in a low spot or behind a wall, because the water gets in and stays. In central Pennsylvania, water that stays in a base is water that freezes, and that is where frost heave starts.

57 stone cannot hold water, because there is nothing in it to hold water. Rain hits it, drops through, and leaves. That makes it the right material anywhere the job is to collect and move water. The same quality makes it a poor base on its own under load. Individual stones roll against each other, the layer shifts, and whatever sits on top moves with it.

Choosing between the two is a matter of which problem matters more in that spot. Under a driveway, stability wins. Behind a wall, drainage wins.

What These Stones Are Called in Pennsylvania

This is where ordering gets confusing. “Crusher run” and “57 stone” are common names nationally, but the quarries in this part of the state use PennDOT spec names, and the person at the counter will expect you to use them too.

Crusher run is 2A modified. Sometimes written 2A mod, sometimes just “modified.” It is the dense-graded limestone base stone that nearly every contractor in central PA uses under patios and driveways. Ask for crusher run at a local quarry and you will probably get pointed to 2A, but asking for 2A modified directly avoids confusion.

57 stone is 2B clean. The “clean” matters. 2B is the PennDOT size designation, and it corresponds closely to AASHTO #57, which is why some suppliers list it as 2B/#57 or just “57s.” If you leave off the word clean, there is a chance you get something with fines in it, which is not what you want for drainage.

A few other names you will hear at the yard, so they do not throw you off:

• 2A without “modified” is a similar dense-graded base, and many yards treat the two as the same thing. Ask if you are unsure.
• 1B or pea gravel is smaller clean stone that drains but rolls badly. It is not a substitute for 2B in a drain or behind a wall.

If you are putting in an order, say what the stone is for. A good quarry counter will steer you to the right name once they know whether you are building a base or a drain.

Where Crusher Run (2A Modified) Belongs

Under anything that carries weight and needs to stay flat.

Driveways. Gravel driveways are often built entirely from 2A, placed in lifts and compacted, then topped with a finer stone for the driving surface. Concrete and asphalt driveways sit on a compacted 2A base as well. Our article on how thick a concrete driveway should be covers what goes under the slab and why the base matters as much as the concrete.

Paver patios and walkways. The standard build is excavation, a compacted 2A base placed in lifts, an inch of bedding sand, and the pavers. The 2A is what keeps the surface from settling and rutting. Depth varies with use, with patios on the shallower end and anything a vehicle drives on needing more.

Shed and pole barn pads, and backfill where settling matters. Same idea. A compacted 2A pad spreads the load, and 2A placed in lifts in a utility trench or under a sidewalk stays put in a way that loose fill or clean stone does not.

The one rule that goes with all of these: 2A has to be compacted. Dumped and raked, it is a pile of stone with dust in it. Compacted in lifts of a few inches with a plate compactor or a roller, it becomes a base.

Where 57 Stone (2B Clean) Belongs

Anywhere water needs to get in and get out.

French drains and trench drains. A French drain is a trench of clean stone around a perforated pipe, wrapped in filter fabric. The stone has to be open-graded or the drain does not work. 2B is the standard. We go into when one is actually needed in do I need a French drain.

Behind retaining walls. Water building up behind a wall is the main reason walls lean and fail. The fix is a foot or so of clean 2B directly behind the block, fabric between the stone and the soil, and a perforated pipe at the base that runs out to daylight. Our article on retaining wall drainage walks through the whole detail.

Under concrete slabs. A few inches of clean stone under a basement floor or garage slab breaks the capillary path, so ground moisture does not wick up into the concrete.

Around foundations and footings. Clean stone against foundation walls, with a drain tile at the footing, is how water gets away from a basement.

Dry wells and downspout burial. The pit that receives roof water is filled with clean stone so the water has somewhere to go while it soaks in.

Leveling pads for walls. This one surprises people, because a leveling pad is a base and bases are supposed to be 2A. Many contractors, Muthler Landscaping & Construction included, prefer a compacted 2B clean pad under segmental block walls. The pad sits at the bottom of the wall, exactly where water collects, and clean stone there does not hold water and does not heave. Other contractors use 2A for the pad and build it tight. Both approaches are common, and either works when it is compacted properly and the drainage behind the wall is right. The block manufacturers publish their own base recommendations, and Allan Block’s installation guides at allanblock.com are a good reference. The whole wall system is covered in our guide to segmental retaining walls.

Open-Graded Base for Pavers: The Other Way to Build a Patio

There is a second way to build a paver base that does not use 2A at all, and it is worth knowing about because it shows up in product literature and in some contractor proposals.

An open-graded base uses clean stone, often 2B or a slightly larger clean stone, for the main base layer, with a thinner layer of smaller clean chip stone instead of sand for bedding. The idea is that water that gets through the joints drops straight through the base and out, so there is nothing to freeze and nothing to heave. The Concrete Masonry & Hardscapes Association, which absorbed ICPI, has published guidance on these systems at masonryandhardscapes.org.

It is a legitimate system, and it is especially attractive in wet, frost-prone ground. The trade-off is that an open-graded base needs well-built edge restraint and a stable subgrade, because the stone itself does not lock. It is not the same as dumping 57s under a patio and setting pavers on them, which is one of the mistakes covered below. It is a designed system with its own bedding and containment details, and it should be built as one.

Ordering: Tons, Yards, and Depth

Quarries sell stone by the ton. Homeowners usually think in cubic yards, because that is how you figure a volume from length, width, and depth. The conversion depends on the stone and how wet it is, but roughly a ton and a half per cubic yard is a reasonable planning number for both. Confirm with the yard before you order, because they know their own material.

To figure the volume, multiply length by width by depth in feet, then divide by 27 for cubic yards. Add 10 percent or so for compaction and waste. Compacted 2A takes up noticeably less space than loose 2A, so a load that looks like plenty in the truck can come up short after the plate compactor.

Depth depends on the use and the ground. Patios generally take less base than driveways, and a soft clay subgrade takes more base than firm gravelly ground. A dense-graded base goes in a few inches at a time rather than all at once, which is part of why depth affects how long the job takes. For drains, the stone depth is set by the pipe and the trench, not by load.

The Mistakes We See Most

57 stone under a patio with nothing to lock it. Someone reads that clean stone drains and puts a thick layer of 2B under their pavers, screeds sand over it, and sets the patio. The sand washes down into the open stone, the pavers settle unevenly, and it never stops moving. Clean stone under pavers only works as part of an open-graded system with the right bedding and edges.

2A under a wall where water sits. A dense-graded pad at the bottom of a wall in a wet spot holds water against the first course. In winter that water freezes and lifts the base of the wall, which is the one place a wall cannot afford to move. If the ground is wet, clean stone at the base and good drainage behind the wall is the safer detail.

Mixing them. Blending 2A and 2B in the same layer gets you a material that neither compacts well nor drains well. If a job needs both, they go in separate layers with a clear boundary, usually fabric, between them.

Skipping fabric where fines meet clean stone. This is the slow failure. Clean stone placed against soil or 2A with no fabric between them gradually fills with fines. A French drain with no fabric clogs over a few years. Drainage stone behind a wall with no fabric turns into a muddy mix and stops draining. Non-woven geotextile between the two is cheap and it is what keeps clean stone clean.

Not compacting 2A. Mentioned above, but it belongs on this list because it is the most common reason a base fails. A base that was never compacted will compact itself over time, under the patio, unevenly.

What a Homeowner Can Do and When to Hand It Off

Ordering a few tons of 2B for a downspout dry well or a short French drain is well within reach for a homeowner with a weekend and a wheelbarrow. So is a small 2A pad for a shed if you rent a plate compactor and take the lifts seriously.

Where it gets harder is scale and consequence. A paver patio base is a lot of stone moved and compacted precisely to grade. A retaining wall base has to be dead level and correctly drained, because every course above it depends on it, and walls over about four feet measured from the bottom of the base generally need an engineer. A driveway base is a lot of tonnage compacted in lifts across a large area. On those jobs, the cost of getting the base wrong is usually a rebuild, and the stone is the cheapest part of the whole thing.

If you are planning one of those and want a second opinion on what belongs under it, Muthler Landscaping & Construction is happy to look at the site and talk through the options, including the parts that make sense for you to do yourself.

Size guides: full materials lists and installed cost for a 12×12 paver patio, 20×24 paver driveway, 40 ft × 3 ft wall, and every other common size.