19 mm Asphalt Mix: Where It's Used

A 19 mm asphalt mix is hot mix built around stone with a nominal maximum size of 19 millimeters, which is 3/4 inch. It's most often used as the binder or intermediate layer, the strong middle course that sits under a finer surface mix. It can also serve as a surface on industrial yards and heavy-duty areas where a smooth look matters less than strength. Because the stone is fairly large, it needs a thicker lift than fine mixes, usually around 2.25 to 3 inches compacted.

What asphalt is made of → Asphalt driveway thickness →

What "19 mm" Actually Means

The number is the nominal maximum aggregate size, or NMAS. It's not the biggest rock in the mix, exactly. Anvilfield's field guide defines NMAS as the sieve one step up from the first sieve that catches over 10 percent of the aggregate.

Common sizes run like this:

• 9.5 mm (3/8 inch): fine surface mix
• 12.5 mm (1/2 inch): standard surface mix
• 19 mm (3/4 inch): binder or intermediate mix
• 25 mm and up (1 inch or more): base mix

Where 19mm Asphalt Mix Gets Used

As a Binder Course

This is its main job. Anvilfield's guide says surface mixes commonly run 9.5 or 12.5 mm while binder mixes often use 19 mm. On a two-layer driveway or parking lot, the 19 mm goes down first to carry the load, then the finer top goes over it.

On Heavy-Duty Surfaces

The HMA Pavement Mix Type Selection Guide, published jointly by the National Asphalt Pavement Association and the Federal Highway Administration as Information Series 128, frames the choice partly around looks. Its text contrasts two settings: a city street, where a finer dense mix with 9.5 or 12.5 mm stone may be chosen, and an industrial area, where 19 mm could be the better fit. The guide is firm that appearance should never win out over performance.

Under Heavier Traffic

The same NAPA/FHWA guide says that as traffic loads rise, a mix with larger stone deserves more consideration. Whether a particular truck apron or loading area gets a 19 mm layer is a design call for your contractor or engineer. For a homeowner, it's most likely to show up in a thicker driveway built for heavy vehicles or as the lower lift of a long private road.

How Thick to Lay It

Bigger stone needs more room to settle into place during rolling. Citing the Asphalt Institute, Anvilfield's guide puts the usual floor at 4 times the stone size for dense-graded mixes, dropping to 3 times when the mix is finer. Four times 19 mm is 76 mm, or about 3 inches. Three times is about 2.25 inches.

The New Jersey Asphalt Pavement Association's design guide is more conservative. It says lift thickness should allow for at least 4 to 6 times the NMAS, and it recommends a minimum lift of 3 inches for 19 mm mix and 2 inches for 12.5 mm. Anvilfield's layer table puts a typical binder lift at about 2 to 3 inches.

Laid too thin, the big stones bridge, the mat tears, and it won't reach density.

How It's Labeled

Plants and state agencies name mixes differently. In New Jersey's system, for example, a designation like 19M64 means a 19 mm mix designed at a medium compaction level with PG 64-22 binder, according to the New Jersey Asphalt Pavement Association guide. If you're reading a quote, look for the millimeter number, or ask the contractor what size stone the lower layer uses.

For how the binder and surface layers split the work, see binder course vs surface course.

Pros and Cons

Pros:

• Strong and stable under heavy loads
• Good for building up thickness efficiently

Cons:

• Rougher, more open texture
• The NAPA/FHWA selection guide warns that larger-stone mixes tend to have a coarser texture and may segregate more easily
• Needs a thick lift, so it's not suited to thin overlays
• Less attractive as a finished surface on a home driveway

Weight and Tonnage

A 19 mm mix weighs about the same as other dense hot mixes, so the standard 145 pounds per cubic foot works for planning, or about 109 pounds per square yard per inch. Say you're putting a 3-inch binder lift on a 600-square-foot pad. That comes to 10.9 tons (600 × 0.25 × 145 ÷ 2,000), and your waste allowance goes on top.

Our rough planning range for dense hot mix is $90 to $130 per ton plus trucking, though prices vary by region and season, so get local quotes (the cost per ton calculator helps), and plants price each mix differently, so ask for binder and surface mix as separate lines. Ask the asphalt plant nearest you what binder mixes it runs, because not every plant makes every size every day.

To see where 19 mm fits among the other mixes, check the asphalt mix types chart.

Is 19 mm Right for a Home Driveway?

For most homes, a single lift of 9.5 or 12.5 mm surface mix over good stone base is plenty. A 19 mm binder makes sense if:

• You'll park an RV, box truck, or trailer regularly
• The driveway is long and carries delivery trucks
• The soil is weak and you need more structure
• You're paving a total thickness of 3.5 inches or more

For the bigger picture of how a residential job goes together, see the overview of asphalt driveways.

Bottom Line on 19 mm Asphalt Mix

A 19mm asphalt mix uses 3/4-inch stone and usually serves as the strong binder layer under a finer surface. It's also used as a surface on heavy-duty and industrial areas. Lay it at least about 3 inches thick, top it with a finer mix on driveways, and confirm with your plant which sizes it produces.