These days, homeowners are faced with a dizzying array of driveway surfacing options, from old fashioned loose gravel to space-age resins.
For homeowners searching for an economical, low maintenance driveway surfacing option the rustic, yet refined look of an oil and stone may be just the ticket.
An oil and stone driveway is a gravel drive surfaced with asphalt (bituminous oil) and loose stone. While the asphalt is fresh, the loose rocks are spread on the surface and pressed into the asphalt by a heavy roller.
If that looks and sounds familiar, there’s a good reason.
Oil and stone surfacing has been used for centuries on rural roads and airport runways.
The sealing drives and roads with oil (or in the early days, coal tar) and stone chips originated in England in the 1830s. As automobiles replaced horse-drawn carriages and distillation of crude oil made bituminous oil readily available, the practice became commonplace throughout the USA, England, Australia, and New Zealand.
Over the years, the technique has acquired many names including, “tar and chip,” “chip-seal,” or, if you’re into old-school British spy novels, “macadam.”
Regardless of what you call it, these types of driveways are a tried and true way to inexpensively and durably surface a drive.
It’s probably worth clarifying a few confusing terms for similar but distinct surfacing options.
What Exactly Is An Oil And Stone Driveway Made From?
The binding agent in an oil and stone road is bituminous oil.
When crude oil is distilled, it separates into different fractions based on the component hydrocarbons’ weight. Gases rise to the top, intermediate weight hydrocarbons like fuel oil and diesel occupy the distillation column’s middle. The bottom of the atmospheric distillation column is bituminous oil.
Many people confuse bituminous oil with asphalt. Bituminous oil (or bitumen) is an immediate resulting fraction of crude oil (as described above).
Asphalt, on the other hand, is the result of blending bitumen, ground gravel, and sand.
The resulting asphalt is heated and poured hot on the desired surface. It is relatively brittle and, on a driveway, will require a sealant. An asphalt driveway is always black and relatively smooth. Most roadways in the USA are asphalt.
An oil and stone surface is also made of bitumen and gravel, but they are applied to the substrate as layers rather than pre-blended layers. The resulting driveway doesn’t need to be sealed and is less brittle.
Another common confusion is tar and bitumen.
Tar is a hydrocarbon distillate from oil, coal or wood. It has a lower melting temperature than bitumen, takes longer to harden and produces a more brittle surface.
The confusion between tar and bitumen is so common that the term “tar and chip driveway” is synonymous with “oil and stone driveway.” However, the prior name is technically incorrect as tar is seldom if ever, used on driveways.
The Stones Used in Oil and Gravel Driveways
The stone used in this type of driveway can be almost any stone depending on the desired look and feel. Popular options include granite, flint, magnesian limestone, slate or river rock.
10 mm is the most popular average stone size, but the size can vary from about 5 mm up to 20 mm. Stones larger than 20 mm bind less effectively and are more likely to become loose over time.
A seminal study of oil and stone surfacing conducted in New Zealand in 1935 established that the ideal ratio of oil to chips should result in the bitumen reaching 2/3 the height of the average stone and that roughly cubical stones are preferable to flat or round rocks.
These basic principles are still the gold standard today.
Advantages of Oil and Stone Driveways
Unfortunately, many homeowners fail to consider because,
- they picture a boring black stone backroad or,
- they assumed there must be some new, better alternative.
Modern oil and stone drives come in a wide range of colors and textures and remain one of the most economical and attractive driveway solutions available.
In modern oil and stone driveways, the owner can choose the color and size of stones used in the top layer.
This allows the homeowner to customize the drive’s look to complement the façade of their house, landscaping, or the surrounding natural stone.
It also creates a country house feel that’s a nice midpoint between plain gravel and the industrial feeling of black asphalt or concrete.
Paver borders upgrade the look even further and help keep loose stones out of surrounding grass and plant beds.
Installation cost of oil and stone driveway
Given the long history of oil and stone roads, it is not surprising that it is among the least expensive driveway options.
They are less expensive because the two essential components, bituminous oil and stone, are readily available and require no sophisticated equipment to store, transport or install.
It will cost significantly more than a gravel driveway. Yet it will be less expensive than asphalt and about 1/2 the cost of concrete or pavers.
Ease of Installation
Oil and stone driveways are not a DIY project. You’ll want to find a qualified professional. But that said, they are relatively easy and fast to install.
The Layers of an Oil and Stone Driveway
As with any drive, your contractor will begin by excavating, grading, and compacting the soil. Then he will deposit a layer of gravel. It is crucial to resolve any slope or drainage issues before installation.
A driveway is only as good as the surface beneath because oil and stone follow the underlying layers’ contours.
If you are installing over a previously existing driveway, ensure that the substrate is not severely cracked and no potholes are present. Oil and stone cannot be used to repair those kinds of defects.
The contractor will then spay a ¼ inch layer of bitumen heated to 190º F over the gravel. Your contractor will need to schedule the spraying on a dry day with an ambient temperature of at least 55º F.
While the asphalt is still hot, the contractor dumps loose stone on top of the bitumen. A crew will then spread the stones by hand using wooden lutes. They will need to do this quickly since bitumen hardens relatively fast.
A special-purpose roller truck or hand-roller presses the loose stones into the hot asphalt, essentially gluing the loose stones together with bitumen. It’s essential to use a roller with rubber wheels. The heavy steel rollers used in highway construction will crush the stones, which radically changes the aesthetics.
The Double-Chip Seal
Some homeowners opt to do a second layer of stone, called a double-chip seal. There is also a process called a “cape-seal,” in which a standard oil and stone driveway is covered by a slurry comprised of bituminous oil, fine aggregate, water and cement.
A cape seal will extend a driveway life by as much as 50%. However, the look is much closer to that of asphalt, which may not be desirable to many homeowners.
Another benefit of a driveway is it may be installed over an existing drive, provided the current driveway is in reasonable condition.
Ease of Maintenance
Once you’ve laid down your driveway, there’s little maintenance required.
Unlike asphalt driveways, oil and stone don’t need to be sealed (or resealed on an annual basis.) During the warm days of Summer, the asphalt naturally softens a bit and effectively reseals itself.
The stones due tend to wander, especially in heavy rains. In the Spring, the homeowner may need to rake up the loose stones and redistribute them.
During warmer days, the loose respread stones are pressed back into the asphalt by the owner’s cars’ normal weight.
Some people opt to spray a sealant to “lock’ the stones in place. This is called a fog seal or “enrichment.”
Several higher-tech options are available for oil and stone driveways using either polymer-modified bitumen or an asphalt “emulsion” (which results from blending liquid asphalt, surfactants and water).
These modified binding materials reduce the release of volatile organic compounds, may help water resistance, and reduce cracking.
However, these higher-tech options are not available from most contractors. They also may add substantially to the cost and do not dramatically increase the driveway’s lifetime.
A typical driveway made with oil and stone will last for seven to ten years with little or no maintenance.
These types of driveways present a coarse surface. Unlike concrete, the homeowner needn’t worry about the drive becoming slippery when wet or icy.
You can safely take the trash down the drive to the curb, and getting up the drive in cars is rarely a problem.
On the flip side, the surface is rough, and some of the stones are sharp. Falls on the rough stone can result in cuts and scrapes. If you have kids, they’ll want to do things like skating or skateboarding someplace else.
A final plus is that they are made entirely from natural materials. Unlike asphalt, the bituminous oil used in oil and stone drives is an all-natural petroleum byproduct. Of course, stones are as natural as it gets.
If you are doing new construction, you may even have the option of recycling the material removed for your foundation for your driveway stone.
These types of driveways do not retain heat from the sun as much as many other driveway surfaces, which can be a real boon to surrounding landscaping.
Potential Disadvantages of an Oil and Stone Driveway
There are some things to look out for:
- Runoff and Drainage – If your drive is steep or in a location where it’s subject to regular flooding or runoff, the stones can come loose more frequently and collect wherever the runoff flows.
That can leave the drive looking bare and patchy.
- Snow Plowing – Snow shoveling can be challenging, and snow plowing this driveway requires some care. If the plow blade is set too low, it will catch and displace the stone surface. Set the snowplow shoes about ½ an inch above the surface.
Leave about an inch of snow because the stone provides plenty of traction.
- Local Ordinances – In some areas, oil and stone is prohibited by local ordinance. If you are contemplating using this style of driveway, be sure to check if they are allowed in your area.
- Requires a Qualified Contractor – As mentioned above, this is not a DIY project. Finding a qualified contractor in your area may be a challenge. Just because these types of driveways are low-tech doesn’t mean just anyone can do it well.
Look for an experienced contractor who can show you a substantial portfolio of past projects. Ideally, find someone who’s done projects you can visit and talk to the owners about their experience.
An oil and stone driveway is viable for almost every driveway situation.
Of course, you have to consider the aesthetic of your property. Oil and stone do lean toward the rustic side.
With all the stone color and texture options, the homeowner may customize the look to match most style homes.
If you are in the market for a new driveway (or plan to refurbish your existing one), be sure to give an oil and stone consideration.