Seal coating asphalt driveways, parking lots, and other paved areas is the process of applying a liquid product over an existing asphalt pavement in a manner that seals the surface and fills small voids and cracks as protection against the elements. Left unsealed, sunlight, wind, and water will gradually cause asphalt to harden and oxidize, and as it becomes more brittle, cracking can occur. Over the space of a few years, asphalt paving can be seriously damaged if it is not periodically sealed.
Seal coating to prevent the effects of weathering is a seasonal rite for many businesses and homeowners. Sealing crews are a common sight in September and October in colder climates, where sealing can help prevent damage from freezing water as well as salts and road chemicals. Sunlight and wind are also highly damaging to asphalt in warmer climates.
Given the expense and environmental concerns, business owners and homeowners are well-advised to ask themselves just how necessary seal-coating is, and how often they should do it.
How Seal Coating Works
There are different forms of seal coating material, but all methods work by a process of cleaning and patching the existing surface, then coating the entire surface of the asphalt with a liquid sealer that forms an impenetrable barrier once it is dry. With the surface seal coat intact, the underlying asphalt is protected from the effects of water, wind, and sunlight that can degrade and harden the asphalt and cause it to crack and crumble.
Types of Seal Coating
There are two main products generally used for seal coating: coal tar sealers and asphalt emulsion coatings. The first one is cheaper but will require more product management when it is being applied. It is more often applied by professional crews. If you are concerned about fuel and chemical spills on the surface, this is the one to use. Asphalt emulsion sealers are easier to apply and they emit fewer volatile organic compounds (VOCs) than regular coal-tar-based products. However, the protective layer is less resistant to chemical spills.
Whatever form of sealant selected, higher levels of solids in the product indicate higher quality sealants. Be sure to verify the manufacturer's recommendations before buying the product, and make sure it is intended for your use.
Two other types of asphalt sealers are acrylic and fast-dry. Acrylic sealers are synthetic compounds comprised mostly of acrylic and polymers. Acrylic sealer is considerably less harmful to the environment and poses fewer health risks to those who work regularly with it. But it is a much more expensive material and some professionals feel that it offers a somewhat inferior protective layer. Fast-dry sealers are usable for foot traffic about an hour after application, and for vehicle traffic in a single day. This is a good option when a business needs to quickly return the driveway or parking lot to service. But fast-dry options do not last as long, and it requires temperatures above 75 degrees Fahrenheit for application.
Benefits of Seal Coating
Seal coating has distinct benefits as preventive maintenance for asphalt paving:
- Extends the life of the driveway and parking lot by preventing the asphalt from hardening and crumbling.
- It creates an attractive, uniform coat over the pavement, especially if crack and holes are properly filled before seal coating is applied.
- Sealing protects the driveway from salts, chemicals, and moisture from entering the pavement
- Seal coats are easy to apply squeegees or sprayers; homeowners or small businesses may be able to do this themselves rather than hiring a firm.
- Seal coating is a cost-effective way of repairing or surfacing the existing pavement, extending the life of the pavement and driveway.
How Often to Seal-Coat
The seal coating process can is normally first applied one year after the initial pavement has been placed to allow proper cure and wear of the surface. After this, it's recommended that you have driveways and parking lots seal coated every two to three years for normal use, or every year if the pavement experiences heavy traffic.
The average cost for the basic materials to seal coat a driveway or parking lot is about 40 cents per square foot for individuals doing the work themselves, although these costs can be higher depending on the equipment you need to purchase. Low-end sealants range from $6 to $9 for a 5-gallon pail that covers about 400 square feet, while top graded products will cost around $25 for a 5-gallon pail that can cover up to 300 square feet.
For professional installation, national averages are about $1.15 per square foot for materials and labor combined. Costs can be higher depending on the amount of surface preparation and repair required. Bear in mind that walls and other obstacles that prevent you from applying the seal coating with a squeegee will significantly add costs to your project.
Organizations such as the USGA (United States Geological Survey) and Baylor University have determined that workers who regularly work with coal-tar are at increased health risk because of exposure to cancer-causing polycyclic aromatic hydrocarbons (PAHs). These risks are most substantial for workers who handle the coal-tar sealers regularly, but these substances are also likely to run off into groundwater supplies if they are applied in excess quantities, which is often the case when individual homeowners or businesses perform the application themselves. Although not yet declared a carcinogenic material by OSHA, the National Toxicology Program considers coal-tar a human carcinogen, and some cities have outlawed the use of coal-tar sealers for asphalt pavement. Major retailers such as Home Depot and Lowes have stopped selling coal-tar sealers, but professional crews often still use it where allowed. If you are an environmentally conscious homeowner or business leader, you may want to ask about this before hiring a company to seal your pavement.
Asphalt-emulsion types of seal coating pose fewer health risks, while acrylic sealers are even safer.
Professional seal coating crews or individual homeowners or businesses follow this general procedure for seal coating:
- Check the weather forecast and select a period when dry weather is expected for at least 48 hours.
- Barricade the driveway or parking lot to ensure that there is no traffic.
- Do a general cleaning of the pavement by sweeping and power washing.
- Oil spot prime all oil spots and apply liquid sealer to deep cracks.
- Patch deep holes with asphalt patching compound, packing it firmly to ensure a flat, solid surface.
- Apply liquid seal coat with a squeegee or sprayer over the entire surface, according to manufacturer's instructions.
- Check for spots missed, and, where necessary, plan for a second coat for the following day.
- After the last seal coat has dried (generally about 36 hours), remove barricades.
- If striping for parking spaces is required, this can be applied after the surface has cured for at least 24 hours.
Once applied, you will need to protect the area for at least 36 hours, although most manufacturers specify 48 hours for the chemical to set and cure. Depending on the manufacturers' recommendation, the right time of the year to seal coat is when temperatures are expected to drop no lower than 55 degrees, which will ensure that the product cures properly. Watch out for leaves and debris that might degrade the emulsion coating once it has been applied and before it has set.
When applying the product yourself, be sure to follow these tips for better performance:
- When the area is large, consider spraying it instead of using squeegees.
- Sand can be mixed with the product to create a non-slippery surface and to provide a little more consistency to the seal-coating product.
- Use a pressure washer to prepare the driveway by cleaning all cracks and removing all debris and vegetation in cracks.
- Seal coating products can be used to cover cracks as wide as 1/8 inch, but don't try to use it on cracks that are wider. Larger cracks should be filled with a product designed for such use before the surface seal coating is applied. Rubberized crack sealer is ideal for repairing such cracks.
- Oil stains should be removed using an oil stain primer prior to applying the seal-coating product.
- Do not expect the seal coat process to fill up potholes. Instead, apply asphalt or pothole fill product to level these areas.
- Before using up one bucket of seal-coating product, blend in the next bucket. There can be subtle differences in colors between buckets, and this method helps you maintain color uniformity over the entire surface.
- Two or more thin coats is better than attempting to apply a single thick coat of sealer. Apply coats in alternating directions—with subsequent coats applied perpendicular to the preceding coat.
- Be careful during application, as seal coat products will stain other areas, such as adjoining concrete surfaces.