Railroad Ballast in Maryland: Answers Before You Order a Pad

Two products on this site get confused with each other more than any others, and they behave in opposite ways. CR-6 is dense graded: everything from its top size down to dust, so it compacts into a bound layer that sheds water across the surface. Railroad ballast is the reverse. Large angular pieces, graded to interlock under load while staying open enough that water leaves through the layer rather than sitting in it. On a soggy Anne Arundel equipment yard that difference is the whole job.

Size: roughly 1 inch to 2.5 inches. Grading: graded to interlock under load while draining freely. Type: large angular crushed stone. Approximate weight, from this site's own published figures, about 2,900 lb per cubic yard, or 1.45 tons per cubic yard.

Is ballast just a coarser version of CR-6?

No, and swapping one for the other is the usual mistake. CR-6 is the material for a drive or a paver base, because the fines in it lock the stone together under a compactor and the result takes a car without moving. Ballast has no such fines. It will not bind, it will never read as a smooth surface, and left exposed underfoot it stays loose. What it does instead is carry weight on ground that would swallow a finer material, while draining hard enough that the base under a pad does not stay saturated through the winter.

Its nearest neighbor in the catalogue is #4 Crushed Stone at about 3/4 to 1-1/2 inches, which does a similar job at a slightly smaller size. Above both sits RipRap, which is armor stone for moving water rather than a load-bearing layer.

Will a hot tub pad on Anne Arundel clay sit level on it?

Not on its own. A hot tub is a concentrated static load sitting on ground where Coastal Plain clay holds water and frost reaches about 30 inches in that county's code. Ballast is the right bottom course there: it spans the soft ground and keeps the base draining. What it cannot do is provide the flat, stable bearing surface the tub itself needs, because stones this size leave gaps a pad will rock on.

The build that works puts ballast at the bottom, a compacted dense-graded layer such as CR-6 above it, and the slab, frame or paver surface on top of that. A worked example, not a real installation: an 8 foot by 8 foot pad taking an 8 inch ballast course. 8 x 8 = 64 square feet. 8 inches is 0.6667 feet, so 64 x 0.6667 = 42.7 cubic feet. 42.7 divided by 27 = 1.58 cubic yards, about 2.3 tons.

Does a side-yard dog run drain better with ballast than with #57?

It drains at least as well, and it stays put better, but it is the wrong surface for dogs. Angular stone this size is hard on paws, it traps whatever needs hosing out of it, and nothing with a top size over two inches is pleasant to walk on. Use ballast as the layer that keeps the run out of the mud and put something finer on top.

Worked example: a run 5 feet wide and 34 feet long, with a 4 inch ballast course. 5 x 34 = 170 square feet. 4 inches is 0.3333 feet, so 170 x 0.3333 = 56.7 cubic feet, divided by 27 = 2.1 cubic yards, about 3.0 tons. The finishing layer over it is a separate order, usually 3/8" Natural Pea Gravel for something rounded underfoot.

How many tons does a 20 by 24 turnaround take?

Worked as an example at a 6 inch course: 20 x 24 = 480 square feet. 6 inches is 0.5 feet, so 480 x 0.5 = 240 cubic feet. 240 divided by 27 = 8.89 cubic yards, which at 1.45 tons per cubic yard is about 12.9 tons.

For any other shape, the arithmetic is the same: square footage, times depth in feet, divided by 27, times 1.45. A circle is diameter times diameter times 0.7854. If the pad is being built in two courses, work them separately, since the lower course of ballast and the upper course of base carry different weights per cubic yard. The stone calculator will do the conversion once you have the cubic yards.

What holds it at the edge of a sloping Piedmont lane?

Something physical, every time. Rolling Piedmont ground sheds storm runoff quickly toward stream valleys, and a loose coarse layer on a grade will travel with it. Three things help: cut the pad or lane into the slope so the uphill side has a shoulder to bear against, put a restraint on the downhill edge, whether that is a timber, a curb or a trench shoulder in firm ground, and take the water off before it reaches the stone with a cross drain or a ditch. On Western Maryland slopes, where rain and snowmelt run fast into narrow valleys, the drainage work matters more than the depth of stone.

Keep the course at the shallow end of what the job needs on any real grade. A deep loose layer creeps; a thinner one over a well drained subgrade stays.

What has to be clear before the truck reaches the gate?

Delivery is arranged at checkout from your ZIP code, and this is a heavy material, so the access matters more than it does on a light load. The truck needs a route in, somewhere it can tip, and room to reverse out with nothing overhead. Ground that is already soft is not where you want a loaded truck standing, which is worth thinking about given why you are buying ballast in the first place.

Mark the drop point with a stake before the day, and if the pad is a long wheelbarrow run from where the truck can reach, ask for the load in two or three piles along the route. Work out your cubic yards, convert them, then set an amount and a date on this page. Where a pad is going in over ground you are unsure about, email the dimensions and a note on the subgrade through contact first.