Reading the surface
Why are there loose stones all over my driveway?
Loose stones coming off the surface is called raveling, and it means the binder holding the top of the asphalt together has worn out.
The numbers
- Raveling is the stage after graying, and it works from the top down.
- Sweeping up grit after every rain is the usual first sign.
- It concentrates where water runs and where tires turn.
- Caught while the surface is still solid underfoot, it is what sealcoating is for.
What raveling is
The stone in asphalt is held in place by a binder. Sun and oxygen break that binder down at the surface, and once enough of it is gone the stones at the top have nothing gripping them. Traffic, a broom, a snow shovel or running water takes them away one at a time.
The surface goes from smooth to open, then to visibly pitted, and the drive starts shedding grit onto the sidewalk and the garage floor.
Where it shows up first
Where water runs and where tires work. The low edge of a sloped drive, the apron at the road, the spot a car turns into every day, and anywhere a downspout discharges onto the surface.
On a lot it is the drive lanes and the turns rather than the parking stalls, because the stalls hold cars sitting still and the lanes take the scrub of every tire that turns.
What can be done about it
While the surface is still sound underneath, the loose material gets swept and washed off, because nothing bonds to a surface that is shedding, and then a coat of sealer replaces the protection the binder used to give.
What sealing does not do is put back the stone that is already gone. A surface that has raveled deep enough to be visibly rough is still rough after it is sealed. What changes is the cause: the coat takes the sun and the water that were breaking the binder down.