#57 Stone in Pennsylvania: Clean 3/16 to 1 Inch Rock

Through the Great Valley and the folded ridges either side of it, the valley floors are shale in some places and limestone or dolomite in others, and the limestone ones weather down to heavy clay that holds water the way a bowl does. Put a pole barn, a drive or a run of wall on ground like that and the question is never whether water arrives. It is whether the water has somewhere to go once it does. #57 stone is the material people order when the honest answer is no.

Angular rock at 3/16 to 1 inch, washed clean of everything smaller

What lands is angular crushed rock graded to the #57 band, running roughly 3/16 inch to 1 inch, with the fines washed out. Push your hand into the pile and you feel individual pieces rather than a mass. Hold a shovelful up and light comes through it. Those gaps between the stones are about a third of the volume of the pile, and they are the reason the material exists: water moves through the layer instead of standing on top of it, and it keeps moving after a wet week in March.

Locally you will hear the same size called 2B, sometimes 2B clean stone, sometimes just three-quarter clean. PennDOT Publication 408, Section 703 sizes clean stone by AASHTO number, and Pennsylvania yards kept the older size names running alongside those numbers, so 2B and #57 describe the same size band in everyday trade use. This site lists them as separate products, so order against the name your contractor or your spec sheet gave you.

#57 Stone against 2B, #67 and 1B on the same order form

Four listings here look similar on a screen and behave differently in a trench.

And then there is the one people reach for by mistake. 2A Modified is the dense-graded base with the fines left in. It compacts into a slab and it does not drain. In a French drain it is the single most expensive mistake on the list, because the fines clog the trench and the whole run stops working within a season.

Why the missing fines are the entire point

Fines do two jobs in a base material: they fill voids and they bind. In clean stone both of those are exactly what you are paying to avoid. Take them out and the stone cannot pack solid, so the voids stay open and water keeps a route through. That also means #57 stone will never behave like a compacted base. It locks together under a plate compactor because the faces are angular, and it will carry weight, but it stays a layer of stone with holes in it rather than a sealed mass.

The practical consequence on limestone valley ground is worth stating plainly. Runoff concentrated off roofs, gutters and drives is what opens sinkholes in karst country. Clean stone in a properly laid drain moves that water along a route you chose. Clean stone dumped into a hole so water can soak away faster is the opposite idea, and it is not one to copy.

Depth for a pole barn pad, a single-car drive and a flagstone run

Under a pole barn or equipment pad, the clean stone layer is usually sitting over a prepared subgrade and under a slab or a compacted base, providing drainage and a capillary break rather than structure. On a drive, the same stone can be the running surface, though it stays loose underfoot and under tires and wants a compacted base beneath it. Under a flagstone walkway, it works as the drainage layer with a thin bedding course of Screenings screeded over it, because setting flagstone directly onto one-inch rock is a way to break flagstone.

The depth guide on the calculator puts landscaping work around 2 inches and driveway work around 4, which is a reasonable starting frame. Drain trenches are set by the trench, not by a rule of thumb: the stone surrounds the pipe and fills the trench, so the depth in your sum is the trench depth.

Working out the cubic yards for a 30 by 40 pad

Hypothetical examples. Area in square feet, times depth in feet, divided by 27.

Reading it the other way around is often more useful. One cubic yard is 27 cubic feet, so spread at 2 inches it covers about 162 square feet, at 3 inches about 108, and at 4 inches about 81. At the weight this site's calculator pages publish for #57 and 3/4 inch crushed stone, about 2,800 lb per cubic yard or roughly 1.40 tons per yard, the pole barn pad comes to 14.8 x 1.40, approximately 20.7 tons, and the single-car drive to 5.6 x 1.40, approximately 7.8 tons. Tonnage is what you buy, so take the cubic yards to the stone calculator to convert.

Booking a clean stone load onto a valley farm lane

Once the figure is settled, choose the quantity and the delivery date on this page. Delivery is arranged at checkout from your ZIP code, and the truck needs a dump spot it can reach and reverse out of. Farm lanes through the ridges tend to narrow past the first gate, so pick the spot for the truck rather than for the wheelbarrow, and pass anything awkward to Pennsylvania Rock Supply through Contact ahead of the date.