Using Number 2 Stone Under an Asphalt Driveway

Number 2 is a large angular stone used as a bottom course in soft ground. It bridges mud better than sand or screenings. It is too coarse to be the last layer under the paver, so cap it with finer dense-graded stone. Quarry size names vary.

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A bottom course, not a finished grade

Number 2 is the name many quarries use for a large angular stone. In a driveway it belongs as a bottom course where the ground is soft. The big pieces bridge mud better than sand or screenings, which pump and shove aside. That bridging is the reason to spend the tons there. It is too coarse to be the last layer under the paver. The voids at the top are large, the screed will not ride a true grade, and hot mix can slump into the holes. Cap it with a finer dense-graded stone so the asphalt has a tight surface to sit on. A thin choke may be part of locking an open top, but it is not a reason to leave the number 2 exposed as the paving grade.

The number is local

Confirm the local quarry's number, because size names vary. A number 2 in one state is not a promise about the sieves in another. Ask for the gradation, or at least ask what the pieces actually are, before you compare a quote from somewhere else. Do not order by the digit alone. If the quarry calls the same rock by a different name, buy the rock that matches the bottom-course job, not the nickname you searched. When you convert tons, use about 1.4 tons per cubic yard only as a planning default on the cubic yards you measured, and let the quarry ticket be the real weight. A heavier large stone can weigh more per yard than the default. Rerun if they give you their factor.

How the cap and the asphalt sit on it

Build the number 2 thick enough to do the bridging, in lifts a roller or plate can compact, not as one loose mound. Then place the finer cap to the grade the paver needs. The asphalt thickness is calculated after that grade exists, at about 145 pounds per cubic foot, and those mix tons are not part of the stone order. If you only buy number 2 and try to pave on it, the yield of hot mix will look poor and the surface will be rough. If you only buy screenings on soft ground, the bottom will not bridge. The two layers answer two problems. Measure each layer's area, including extra width past the future asphalt edge if you are building that support, and keep each ticket with the layer it belongs to.

A practical sequence

Use number 2 as a large angular bottom course on soft ground.
Cap it with finer dense-graded stone before asphalt goes down.
Ask the quarry what their number 2 actually is, because names vary.
Plan stone near 1.4 tons per cubic yard, and trust the quarry ticket for real weight.

The mistake to skip

Paving asphalt directly on uncapped number 2 stone.

Questions people ask

Can number 2 be the only base under asphalt?

It can bridge soft ground as a bottom course, and it is too coarse to be the last layer under the paver. Cap it with a finer dense-graded stone so the grade is tight. Confirm the local size name before you order. The quarry ticket is the real weight.

Is number 2 the same size everywhere?

No. Quarry numbers are local. Ask for the gradation or a plain description of the pieces. Ordering a digit from a different state can deliver the wrong rock. Match the stone to the bottom-course job, then convert the measured thickness to planning tons.

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