Sealcoating
What is sealcoating?
Sealcoating is a thin coat of asphalt emulsion spread over paved asphalt to keep water, sun and fuel out of the surface underneath it.
The numbers
- Sealer is a coating over the asphalt. It adds no strength and no thickness worth measuring.
- A driveway in northwestern Wisconsin is normally resealed every two to three years.
- Cars usually go back on after 24 hours and heavier vehicles after 48.
- Sealer does not bridge an open crack, lift a low spot or repair a failed base.
What the coat is doing
Asphalt is stone held together by a binder that came out of the ground as oil. Sun, oxygen, water and gasoline all attack that binder. As it goes, the stone at the surface loses its grip and starts letting go, and water starts reaching the compacted base underneath, which is the part actually holding your cars up.
A coat of sealer puts a sacrificial layer between the weather and the binder. It wears instead of the asphalt wearing, and you replace it every couple of years for a small fraction of what the asphalt costs.
Where sealer stops being the answer
Sealer is thin. It goes on as a liquid and dries to a film, so anything that moves under it keeps moving and anything open under it stays open. A crack sealed over changes color and reappears through the new surface within weeks. An area that flexes under your foot has a base problem and a coat of sealer hides the evidence for a season.
That is why the order matters. Repairs first, drainage second, hot rubber in the cracks third, and the sealer last, once the surface under it is sound.
What is in the material
Two families of sealer are sold in Wisconsin. Coal tar sealer is a byproduct of steel making. Asphalt emulsion is asphalt and water with clay and sand in it. Both go on the same way and both look the same on day one.
Black Widow Sealcoating runs an asphalt emulsion. A homeowner who wants to know which one is going on their drive should ask, because the answer is not visible once it is down.