#67 Stone in Maryland: Choosing It Over #57 and #8

Almost everyone who lands on this page is choosing between three numbers rather than deciding whether to buy washed stone at all. The ground around a Towson or Bowie foundation drains slowly, the trench is dug, and the question is whether #67 stone, the #57 next to it in the list, or the smaller #8 is the right fill. The honest answer is that all three drain, and the difference is how tightly they pack around a pipe, how easily they shovel into a narrow trench, and how they finish where they will be seen.

Size: 1/4 inch to 3/4 inch. Grading: #67. Type: angular crushed stone. Approximate weight, from this site's own figures, about 2,800 lb per cubic yard, or 1.40 tons per cubic yard.

Digging drains between thunderstorm season and the first hard freeze

Drainage work in Maryland gets done for a reason, and the reason is usually a wet basement wall in March or a summer thunderstorm that put water somewhere it should not have gone. That pushes the job into late summer and autumn, which is the best of the year for it anyway. The ground is at its driest, trench walls stand up, and there is time to backfill and settle before the freeze.

The window closes at different points across the state. Garrett and Allegany county codes set frost at 36 inches and the cold arrives early, so trenching there wants finishing well before the first hard freeze. Most Piedmont counties work to 30 inches. Several Eastern Shore counties set 24 inches, with Cecil at 32, but on the Shore what stops work is a high water table rather than frost: a trench cut below it fills from underneath and never falls anywhere useful.

Staging the trench, the fabric and the pipe before the stone lands

A washed stone trench is mostly preparation. By the time a load arrives, the run should already be dug to a consistent fall, the trench lined with a geotextile that laps over the top once the stone is in, and the pipe laid on a bedding layer rather than dropped on bare soil. Stone goes in around and over the pipe, then the fabric closes.

Skip the fabric on Maryland ground and you buy yourself a few seasons at best. Piedmont silt and Coastal Plain fines migrate into clean stone from the trench walls inward, and once the voids are plugged the drain stops working even though the stone inside it looks untouched.

Foundation drains, pipe bedding and concrete on a Piedmont lot

• Perimeter and foundation drains, where the smaller top size packs closer to the pipe and around fittings than a coarser stone manages.
• Bedding and backfill for water, sewer and utility lines, supporting the pipe evenly while letting water past.
• Infiltration trenches and stormwater work, where a consistent gradation keeps the flow rate predictable.
• Concrete, where a finer coarse aggregate places and finishes more easily than a larger stone, which matters on exposed or decorative work.
• Visible beds, tree rings and borders, where the even size gives a tidier finish than a mixed stone.

On rolling Piedmont ground the drainage problem is usually surface water arriving fast off a slope, so a drain here intercepts and carries rather than soaks away. On the flat Coastal Plain the problem is water that has nowhere to go, and the design question is where the run discharges, not how big the stone is.

Tons for a 55-foot foundation drain and two smaller jobs

Cubic feet divided by 27 gives cubic yards; multiply by 1.40 for tons at the approximate weight above. Every one of these is a worked example rather than a real project.

• Foundation drain, 55 feet of trench, 18 inches wide and 24 inches deep: 1.5 x 2 = 3 cubic feet per foot of run. 55 x 3 = 165 cubic feet. 165 divided by 27 = 6.11 cubic yards, about 8.6 tons.
• A low spot in a gravel parking area brought back up, 16 feet by 20 feet at 3 inches: 16 x 20 = 320 square feet. 3 inches is 0.25 feet, so 320 x 0.25 = 80 cubic feet. 80 divided by 27 = 2.96 cubic yards, about 4.1 tons. This one works because the water simply needs to get through; for a surface that has to lock up under tires, order CR-6 instead.
• The outlet of a yard drain, 10 feet by 5 feet at 8 inches: 10 x 5 = 50 square feet. 8 inches is 0.6667 feet, so 50 x 0.6667 = 33.3 cubic feet, divided by 27 = 1.23 cubic yards, about 1.7 tons. Where the outlet carries real storm flow and the bank is scouring, this size will move and the job wants RipRap.

Awkward shapes come apart into rectangles, triangles and circles. A triangle is base times height divided by two; a circle is diameter times diameter times 0.7854. Add the square footage, apply one depth, then send the result through the stone calculator for the conversion.

What a #67 drain asks of you after the first nor'easter

Very little, if the fabric went in and the discharge point is clear. Walk the outlet after the first heavy storm and again after the first freeze, and look for two things: standing water at the low end, which means the fall or the outlet is wrong rather than the stone, and silt fanning out of the pipe, which means something upslope is feeding sediment into the run. Bare soil, a downspout emptying onto ground, or an unwrapped trench wall are the usual culprits, and none of them is fixed by digging the stone back out.

Measure the run, work the cubic yards, then set a quantity and a delivery date here. If the trench changes depth along its length, send the two end measurements through contact and have the figure checked before you commit.