What is sealcoating, and why does it matter?
Short answer
Sealcoating is a thin protective coating applied over asphalt. It shields the binder that holds the stone together from UV, water, oil, gas and other chemicals, which slows the oxidation that turns a driveway gray, brittle and cracked — and it puts the black back. It is maintenance for sound pavement, not a repair for broken pavement.
Answered by Sean McCullough, owner of FGG Sealcoating · Serving Delaware County, Pennsylvania and Chester County, Pennsylvania
What actually wears out on a driveway
Asphalt is stone held together by a black, oil-based binder. The stone does not wear out. The binder does. Sunlight dries it out from the top down, and as it dries the surface fades from black to gray, turns brittle, and starts to let go of the stone at the surface.
Once that starts, water does the rest. It gets in through the gaps the binder has left, reaches the base underneath, and in a Pennsylvania winter it freezes and expands there. That is how a tired-looking driveway becomes a cracked one.
What the coating does
A sealcoat is a layer over the top that takes that punishment instead. It blocks UV from reaching the binder, sheds water rather than letting it soak in, and stops oil, gas and other chemicals sitting directly on the asphalt, where they soften it.
It is designed to wear away. A coat that has worn thin in the wheel tracks after a couple of seasons did its job — the wear went into the coating and not the driveway. That is why it gets reapplied on a cycle, and why how often matters as much as whether.
What it does not do
Sealcoat is a coating, not a filler and not new asphalt. It will not close a crack wider than about a quarter inch, it will not fill a pothole, and it will not hold together a driveway whose base has failed. Those are repairs, and they come first — see will sealcoating fix cracks and potholes?
The best time to start sealing a driveway is while it is still in good shape. Coating protects what is there; it does not bring back what is gone.
Related questions
Is sealcoating just cosmetic?
No, though the color is the part people notice. The job it actually does is keep UV and water off the asphalt binder. A driveway that has gone gray has lost binder at the surface, and the loose stone that follows is what a coating is there to prevent.
Is sealcoating the same as resurfacing?
No. Sealcoat is a coating a few millimetres thick over the existing asphalt. Resurfacing lays a new layer of asphalt on top. A driveway with a failed base or widespread breakup needs repair or resurfacing; coating it changes the color and nothing else.
What does sealcoating protect against?
Sun, water, and spills. UV dries out the binder, water gets into the base through the gaps that leaves, and oil, gas and other automotive fluids soften asphalt where they sit. A coating takes that wear so the asphalt underneath does not.