#4 Crushed Stone in Pennsylvania: The Open Layer Under Everything Else

A load of #4 does not look like something you would build a driveway with, and people say so when it lands. Across the ridge and valley country, where valley floors are shale or limestone clay and the anthracite towns sit on ground broken up by old strip workings, this is usually the first stone to go down on a soft spot and the last one anybody expected to be handed. It is worth understanding what you are looking at before deciding it is the wrong material.

#4 Crushed Stone in the hand: fist-sized, angular, impossible to rake flat

The pieces run about 3/4 inch to 1-1/2 inches, crushed rather than rounded, with flat faces and sharp corners. There are no fines in the pile. Tip a bucket out and the stone clatters rather than slumps, and you can see daylight through the heap, because the voids between pieces this size are large and stay large.

Rake it and the rake rides over the top. Walk it and your boot turns. That is not a fault. Those big open voids are the entire purpose: water passes straight through the layer rather than sitting in it, and the angular faces wedge against each other so the mass stays put under a load that would shove rounded stone sideways.

Where a valley lot with wet, broken ground actually needs it

The job is the layer nobody sees. Under a driveway, an equipment pad or a barn approach on ground that holds water, a lift of #4 gives the water a route out of the structure and gives the finer material above something firm to be compacted against. On ground softened by a spring or by old disturbed fill, it also acts as a separation: the large stone bridges across the soft material instead of sinking into it the way a fine base does.

The other uses follow the same logic. It fills gabion baskets because it is too big to wash out through the mesh. It lines ditches and armors channel bottoms where flow is more than a trickle. It makes a construction entrance that shakes mud off a tire. In all of these, size and openness are doing the work.

Two of these three jobs would be ruined by 1-1/2 inch rock

A hot tub pad. Only as the bottom lift. A tub full of water and people is a concentrated, unforgiving load, so what sits directly under the base or slab must be a compacted, dense-graded layer of 2A Modified, with the open stone below it on wet ground. Never set a tub base straight onto #4.

A side-yard dog run. No. Sharp 1-1/2 inch rock is hard on paws and impossible to clean, and nothing about it suits the job. Build a compacted base and finish it with Screenings for a firm surface, or 3/8" Natural Pea Gravel if you want something rounded underfoot.

A turnaround or parking pad. Yes, underneath. The turnaround is where this stone belongs on a domestic property: an open sub-base lift on the soft valley ground, a compacted modified layer over it, and whatever surface course you want on top.

Telling it apart from the ballast above and the 2B below

Three listings sit in a line by size, and the gaps between them are smaller than the names suggest.

Ballast overlaps at the top of this size and is graded to interlock under heavy repeated loading. 2B is the everyday clean stone for trench and backfill work, small enough to shovel comfortably and to bed against a pipe. #4 sits in between and is chosen when the layer has to carry weight and pass a lot of water at once.

Planning the lifts on shale valley floor and stony ridge soil

Think in layers, not in a single number. On firm ground a drive may need nothing more than a compacted base and a surface. On a wet shale valley floor, or across disturbed ground in the coal region, an open lift of #4 underneath changes how long the whole build lasts, and a working figure for that lift on a domestic job is around 6 inches. The compacted layer above it is usually 4 inches or more, and the surface course above that again.

Lay a geotextile separation fabric between soft subgrade and the stone. Without it, wet clay pumps up into the voids under traffic and the open layer quietly turns into a layer of rock and mud. Frost through this belt commonly reaches about 36 inches, set by each municipality, so no practical driveway is built below frost. Keeping water out of the structure is the available strategy, and the open lift is how it is done.

Tons for a 24 by 24 turnaround and an 8 by 8 tub pad

Hypothetical examples. Square feet times depth in feet, divided by 27, gives cubic yards. This site publishes #4 stone and ballast at about 2,900 lb per cubic yard, or 1.45 tons per yard, and road base at about 3,000 lb, or 1.50 tons per yard.

One cubic yard of this stone spreads over roughly 54 square feet at 6 inches, so the turnaround figure is easy to sanity-check. Measure your own area and run it through the stone calculator, which uses the same weights and adds up to five areas at once.

Where a load of 1-1/2 inch rock can be dropped

Big stone is the most awkward material on this site to move after it lands, so the drop spot deserves more thought than usual. Ideally the truck tips it on or beside the area it is going into. A shovel is nearly useless against it, a fork or a bucket is what actually moves it, and a wheelbarrow takes a fraction of what you would load with gravel.

Set quantity and date on this page. Delivery is arranged at checkout by ZIP code, and the driver needs a firm level spot, room to reverse and clear height overhead. Where the lane narrows between a bank and a ditch, tell Pennsylvania Rock Supply through Contact before the date.