Sealcoating fills surface voids, which reduces exposure to oxygen and UV rays. It also reduces the depth to which oil and gas can penetrate the asphalt. It acts as a waterproofing agent, minimizing the rate that the water enters the asphalt of your driveway or parking lot. As a general rule, you should seal your driveway every three to five years. More specifically, if you can see the color of the individual stones that make up your asphalt surface, you know it is time to fill the cracks and reseal the asphalt. Ideally, you want your sealer to be on your driveway for at least 48 hours before any rain comes down on it.