Q–It’s time for a new driveway at my house. I really like the look of gravel but I don’t want the dust. Blacktop is simply too plain. I have seen roads constructed using asphalt and small gravel. Can this be done on a residential driveway? Is it practical? What about the cost?
A–You bet such a driveway is possible. That’s exactly the type of driveway I have. Locally they are called “tar and chip.” Some installers refer to them as “seal chip” or “shoot and chip.” No matter what you call them, they are a dynamic, beautiful surface.
I happened to use two distinctive brown gravels, one from the Meramec River in Missouri and one from an Indiana location. Similar gravel may be available in your city.
A tar and chip driveway is very similar to standard blacktop in composition. Both types of driveway use asphalt cement as the ingredient that creates adhesion to the aggregate.
Blacktop is mixed at a central plant. The asphalt cement completely coats the large, small and fine pieces of aggregate.
Tar and chip surfaces combine either a special cutback liquid asphalt cement or an emulsified asphalt cement and small, similar-sized pieces of clean, angular, washed gravel. These ingredients are mixed together at your house.
Tar and chip surfaces were standard fare on virtually every highway in the U.S. before 1935. Central mixed blacktop technology was just beginning at this time.
Tar and chip surfaces are a wonderful alternative that is unfortunately being left by the side of the road. The contractor applies the hot, liquid asphalt to a standard gravel base or your existing driveway if it is in good shape.
Such driveways usually spread one half gallon of asphalt per square yard. Next, small, cube-shaped pieces of gravel are immediately embedded into the liquid asphalt. Often, this gravel is applied at a rate of 40 to 50 pounds per square yard. This gravel is then rolled and compacted into the asphalt. It is not uncommon for two layers to be installed. That is what I did.
The completed surface differs from blacktop as well. The tar and chip surface is almost always rougher, which provides excellent traction. Unlike blacktop, this surface isn’t black. It’s the color of the gravel you choose.
These driveways can only be installed in favorable weather conditions. Hot, dry weather is ideal. If the weather is too cool, the asphalt cement may cool and set up too rapidly. Then the gravel may not achieve sufficient adhesion. Rain can wash away an emulsified asphalt before it cures.
These driveways have a unique feature. They can heal themselves if a small crack develops. In hot weather, the asphalt cement can flow into the crack and work in conjunction with the loose stones to disguise the imperfection.
These surfaces are inexpensive. Often they cost less than half that of standard blacktop. Unlike blacktop, they never have to be sealed. The service life of a single-coat job is often 8 to 10 years.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352.
