Why do oil stains need treating before sealcoating?

Sealer does not bond to oil. Coated straight over, an oil or transmission-fluid stain shows through and the coating on it lifts. The stain has to be cleaned and primed first.

Does prep really matter that much?

It is most of the job. The coating itself goes on quickly; getting a surface it will actually stick to is the work. It is also the part a cheap quote tends to leave out.

What should I move before the crew arrives?

Everything on the driveway: cars, bikes, bins, planters, basketball hoops, doormats at the garage edge. Cars also need to be parked somewhere they can stay for 24 to 48 hours afterwards.

What prep is involved before sealcoating?

Short answer

Proper prep means cleaning the surface, treating oil and fluid stains so the coating bonds, clearing vegetation from the edges and joints, and filling cracks — all before the coating goes on. The owner’s part is having the driveway completely empty of vehicles and everything else.

Answered by Sean McCullough, owner of FGG Sealcoating · Serving Delaware County, Pennsylvania and Chester County, Pennsylvania

What proper prep involves

A coating is only as good as the surface under it. Before any sealer goes down, a properly prepared driveway has had:

Cleaning. Dirt, leaves and grit swept and blown off, and power washed where the surface needs it. Sealer laid over dirt bonds to the dirt.
Oil and fluid stains treated. Oil, gas and transmission fluid stop the coating from bonding. Stains are cleaned and primed so the coating stays put over them.
Vegetation cleared. Grass and weeds growing along the edges and up through joints removed, so the coating reaches the edge of the asphalt.
Cracks filled. Anything wider than about a quarter inch filled with crack sealant first. See will sealcoating fix cracks?

Questions worth asking about a quote

Because prep is where the time goes, it is also where quotes differ most. A fair comparison between two sealcoating quotes asks the same things of both:

Is the surface cleaning included, and does that include power washing?
Are oil stains primed, or coated straight over?
Are cracks filled first, and with what?

What to have done on your side

The driveway needs to be completely clear. That means every vehicle out — parked on the street or elsewhere, where it can stay for a day or two while the coat cures — and anything else sitting on the asphalt moved off it.