Q: The top few feet of my asphalt driveway slope down 3 in. below the outside edge of my garage floor. Will the rest of my driveway start sinking too? What can I do to fix this?
Rob Haase, Norwood, OH
A: The strip of driveway that is sinking directly in front of your garage is called the garage apron. A sinking garage apron is a common problem that is almost always caused by poorly compacted base material under the pavement. Whether the rest of the driveway will sink depends on how your garage and driveway were constructed. But the chances are good that the sinking problem will be limited to the apron.
When a typical garage is built, the ground is excavated a few feet beyond the garage foundation perimeter. The ground under most driveways is often leveled but not excavated. After the foundation is built, the extra few feet that were excavated around the foundation are backfilled to create a surface that is flush with the driveway base. The backfill must be fully compacted or it is likely to settle over time, resulting in a sunken garage apron.
This problem is made worse and accelerated if water sources (such as downspouts or ground that is graded back toward the driveway) run behind or under the sides of the apron. Water run off will wash out back fill and can freeze, causing the apron to heave and then sink lower when the ground thaws.
The best solution for a sunken apron is to cut out the old apron a few feet in front of the garage and replace it with properly compacted base material and a new apron, which can be made of concrete or asphalt. Concrete is more expensive, but it will last longer and withstand greater weight loads. You can hire a concrete contractor or do the job yourself (see photos 1 through 3 below). Asphalt is less expensive and should be installed by professionals (photo 4, below). It’s not as durable as concrete, but with proper installation and maintenance it should last at least 10 years.
In either case you must resolve any water runoff issues that are contributing to the problem. Re-route or extend downspouts away from the apron, and direct the surrounding grading away from the apron.
Another alternative method for raising sunken concrete aprons is pumping liquid concrete under the slab, a process known as “mudjacking.” The problem with this method is that it doesn’t correct any underlying poorly compacted base problems, so a “mudjacked” apron may sink back down within a few years.