Many owners of asphalt (blacktop) driveways do their own maintenance, patching cracks, filling potholes and applying sealer coats. Unfortunately, this maintenance sometimes doesn't work out well, and in some cases it can actually harm the driveway.

Sealing is the trickiest part of maintenance. According to many experts, some owners apply sealer to new driveways too soon and to older driveways too often. There are a number of other frequent errors made in sealing, some of which could be avoided simply by carefully reading the instructions on the sealer container.

Asphalt driveway sealers can serve some good purposes if properly applied. They improve the appearance of the driveway, at least for a while, and can help reduce penetration and damage from dripping oil and other material. Some sealers contain fine grit or sand that can seal small cracks and reduce water penetration, and improve traction on the driveway.

Here are some tips for successful sealing:

* Don't seal a new asphalt driveway until it has cured for at least a year. Some contractors recommend waiting two to five years. Applying a sealer too soon can prevent proper curing and hardening of the driveway by keeping solvents from evaporating. I had my asphalt driveway resurfaced about three years ago and still haven't sealed it. It remains in excellent condition.

* Don't seal an existing driveway every year. An excessive buildup of sealer can do more harm than good. Sealing every two years is sometimes recommended, but I think three-year intervals are adequate.

* Check out new types of sealers before buying. Sears has a new Weatherbeater Premium Driveway Sealer and Filler that dries black instead of a dull slate gray (the color of many sealers when they dry). This sealer sells for about $16 for five gallons and has a three-year warranty. Home Depot has a product called Latexite Optimum (about $20 for five gallons) that has an eight-year warranty.

* Pick an appropriate time for applying the sealer. Most sealers are best applied when temperatures are between 70 and 85 degrees, with nights that don't fall below 50 degrees. Don't seal a driveway if rain is expected within 24 hours (48 hours is better). A heavy rain too soon can wash off much of the sealer. High humidity can also lengthen the curing time.

* A single thin coat of sealer is best. It should be brushed out to prevent puddles or thick spots that will hamper curing.

* When sealing, don't wear any clothes, including shoes, that you are not willing to throw away. No matter how careful you are, you are almost certain to get spattered by sealer. I recommend long pants and a long-sleeved shirt. Also wear gloves and goggles.

* Stay off the driveway for at least 24 hours after sealing -- longer if possible. When you feel the driveway is ready for use, test it by walking on a small area, then walk on a piece of cardboard or newspaper to see if any sealer sticks to your shoes. If it does, more curing time is needed.

* Above all, read the specific directions for the sealer.

Before sealing, clean the driveway and make any necessary repairs. Various cleaners and sealers for stains are available at home centers and hardware stores. If you have a leaf blower, use it to remove loose dirt and debris such as leaves and pine needles. Sweep with a broom if no blower is available.

Fill holes with blacktop cold patch, sold in bags and applied with a shovel or trowel. Tamp down the patch with a piece of 2-by-4 or another suitable tamper. These patched areas should not be sealed for at least 90 days -- work around them if you seal before that time has passed.

Smaller cracks can be sealed with asphalt crack fillers. These are sold in cans and small tubs for application with a trowel, in jugs for pouring, and in caulking-gun cartridges. I have tried many of these crack fillers and most of them do not last very long -- they shrink or come loose and the crack opens again. I have found that the best crack fillers are usually those that cost the most, generally silicone rubber sealers designed for asphalt.

Questions and comments should be sent to Gene Austin, 1730 Blue Bell Pike, Blue Bell, Pa. 19422. Send e-mail to doit861@aol.com. Questions cannot be answered personally.