Sealing a driveway serves an important purpose in protecting and extending the life of the pavement. However, it is not intended to fill existing cracks and repair damage. Sealing creates a protective barrier on the surface of the driveway that prevents water, chemicals, and UV rays from penetrating the pavement and causing deterioration. But it does not have the viscosity or volume to fill cracks and holes in the driveway surface. So while sealing is an essential part of driveway maintenance, it must be paired with crack filling for the best results.
What is driveway sealing?
Driveway sealant is a liquid substance that is brushed or sprayed onto the surface of asphalt or concrete driveways. It is formulated to be thin enough to penetrate the pores in pavement and create a protective barrier. There are two main types of driveway sealers:
- Asphalt emulsion sealers – These are water-based and made from refined coal tar pitch, asphalt cement, clay fillers, latex polymers, and other additives. Asphalt emulsions allow water to escape through evaporation but prevent liquids from seeping down into the driveway material.
- Coal tar sealers – Coal tar pitch is derived from coal and has a thicker, more viscous consistency. It forms a protective shell on top of the driveway surface.
Most driveway sealant products available at home improvement stores are asphalt emulsion types. Coal tar sealers are more likely to be used by professional driveway contractors due to their stronger protective qualities.
How does driveway sealing work?
When sealant is applied properly to a clean driveway surface, it will soak into the pores and crevices forming a protective barrier. Asphalt and concrete are porous materials containing many microscopic holes. Over time, moisture seeps into these pores expanding when it freezes and contracts when it thrives. This continual cycle of freezing and thawing causes cracks and deterioration.
Sealant penetrates the top layer of the driveway to fill in the pores and create a flexible barrier. This protects against freeze/thaw damage as well as the damage caused by deicers, car fluids, UV rays, and general wear and tear. However, sealants do not have enough body to move into larger cracks or gaps in the pavement.
Can you fill cracks with sealant?
While driveway sealants may penetrate slightly into very fine cracks on the surface, they do not have the viscosity or volume to fill larger cracks or spalled areas in asphalt or concrete. Using sealant alone will not repair cracks wider than 1/4 inch or areas where concrete is missing. The American Concrete Institute recommends repairing cracks wider than 1/4 inch before applying any type of sealer or coating.
If cracks and holes are not repaired before sealing, the sealant will inevitably break down faster in these weak spots. Water and debris will penetrate the thin layer of sealant and continue damaging the pavement underneath. Any thin coat of sealant applied over cracks is just a temporary and shallow fix.
Why cracks must be filled before sealing
Filling cracks before sealing a driveway is important for several reasons:
- Stabilizes cracks – Filling cracks with a flexible material like caulk prevents them from widening from continual freeze/thaw cycles and traffic.
- Structural repairs – Deep cracks and spalled areas can undermine the driveway structure. Filling repairs this damage.
- Prevents further cracking – Unfilled cracks allow moisture penetration that will lead to more cracking as freezing moisture expands.
- Improves appearance – Repairing cracks creates an even surface for a aesthetically pleasing new sealant coating.
- Saves money – Proper crack filling extends the life of pavement and sealant so repairs are needed less often.
How to fill cracks in driveways
The process for filling driveway cracks involves cleaning out debris, applying crack filler, smoothing, and allowing proper curing time according to product specifications before applying sealer. Here are some guidelines for filling various types of cracks:
Hairline cracks
Very fine hairline cracks less than 1/8 inch wide typically only require sealing. The sealant material will adequately penetrate these small fissures.
Narrow cracks
Cracks between 1/8 to 1⁄4 inch can be filled with liquid crack fillers that are brushed or poured into the openings. Choose asphalt-based products for asphalt driveways and concrete/epoxy fillers for concrete. Completely fill the cracks and allow to cure fully before sealing.
Medium cracks
Wider cracks from 1⁄4 inch to 3⁄4 inch should be filled with caulk-type crack repair products. They are available in tubes that can be applied with a caulk gun. Use a rubber squeegee to push the caulk fully into the crack before smoothing.
Large cracks and spalled areas
Cracks wider than 3⁄4 inch and holes or missing pavement will require patching. Remove loose material and debris with a wire brush and chisel. Apply a concrete or asphalt patch material, tamping it down well and allowing proper cure time. For larger patches you may need to apply in several layers.
Seams and joints
Seal expansion joints and seams where the pavement abuts walls or curbs. Use a flexible polyurethane or asphalt-based caulk to allow for continued expansion and contraction.
Best practices for crack filling
To ensure repairs are effective, keep these tips in mind:
- Clean cracks thoroughly and remove all vegetation and debris with a pressure washer or wire brush.
- Make sure surface and cracks are completely dry before applying fillers.
- Use the appropriate filler for each crack width and driveway type.
- Completely fill cracks flush to the surface. Do not leave unfilled areas.
- Allow adequate curing time before sealing. This can range from 2 hours to 2 days.
- Repair any new cracks that appear before sealing. Existing cracks will continue spreading if not filled.
- Wider temperature windows are best for repairs so materials remain viscous enough to spread.
Order of operations: Crack filling then sealing
It is always best practice to fill cracks before sealing a driveway. This order of operations ensures repairs are structurally sound and long lasting:
- Clean – Use a pressure washer or stiff brush to remove dirt, debris, oil stains, and all vegetation from cracks and driveway surface.
- Fill – Use appropriate caulks, epoxies and patch materials to thoroughly fill all cracks. Allow curing based on product instructions.
- Seal – Apply a fresh coating of sealant according to manufacturer specifications. Asphalt emulsion sealers often require two coats.
Benefits of filling cracks before sealing
Filling cracks and repairing damaged pavement before applying sealant has many advantages:
- Prevents premature sealant failures and flare ups at cracks
- Provides an even, smooth surface for the sealant film to adhere to
- Stabilizes cracks so they do not continue spreading
- Reduces moisture penetration through cracks into subsurface
- Lengthens the life of pavement and sealant coatings
- Improves appearance of the finished sealed driveway
- Saves money by reducing the frequency of repairs needed
How long does crack filling last?
The lifespan of repaired cracks depends on the quality of the filler material used, the proper preparation of the cracks, and environmental factors. However, quality caulk-based crack fillers and epoxy repairs typically last 2 to 8 years. Filling cracks before sealing also elongates the life of the sealant. So products applied in the proper order will last longer than using either treatment alone.
Can you seal over cracks?
Simply sealing over unrepaired cracks with driveway sealer provides only partial, temporary protection. While thin sealants may initially hide hairline cracks, they will not prevent moisture intrusion into the pavement. Water will continue to penetrate the substrate, leading to widening cracks, alligatoring, spalling and continued deterioration.
Applying sealer over unfilled cracks also often leads to bubbling, flaking and rapid failure of the sealant in the cracked areas. For best results, all cracks wider than 1/8 inch should be properly filled before sealing a driveway.
Signs you need crack filling
Here are some signs it is time to fill cracks in your driveway before applying fresh sealant:
- Existing sealant is flaking or peeling at cracks
- Networks of fine spiderweb cracking covers large areas
- Long snaking cracks run across or along the driveway
- Spalling has caused small holes and missing pavement
- Cracks are 1/8 inch or wider
- Weeds are growing from dirt in cracks
- Cracks run parallel to the edges or seams in paving
- Water puddles in cracks or indented areas
Cost to fill cracks before sealing
Filling driveway cracks costs approximately $.75 to $3 per linear foot depending on crack width and depth. Materials for cracks under 1 inch cost $5 to $20 while large spalled areas are $10 to $30. A long winding crack 100 feet long would cost about $100 to $300 to fill. Combining crack repairs with sealant application is the most cost effective. Sequential sealant-only treatments wear down faster.
Sealing over unrepaired cracks – Pros vs cons
Here is a comparison of the pros and cons of sealing over cracks versus filling them properly:
Sealing over cracks
Pros
- Initially hides unsightly cracks
- Quick and easy application
- Less labor intensive than filling cracks
Cons
- Does not prevent ongoing subsurface damage from water
- Sealant will fail prematurely at unrepaired cracks
- Can lead to slippery, unsafe conditions as sealant peels
- Does not improve or extend pavement life
- Prone to weed growth as seeds get trapped under sealant
- Costly and frequent reapplication needed
Filling cracks before sealing
Pros
- Stabilizes cracks and prevents further cracking
- Blocks water penetration through cracks
- Provides even surface for smooth sealant adhesion
- Extends pavement life by preventing freeze/thaw damage
- Saves money by increasing time between repairs
- Creates safe surface without bumps or sudden dips
Cons
- More time consuming than just sealing over cracks
- Proper materials and preparation required
- Repeat filling needed as cracks reappear over time
Will sealing make cracks worse?
In most cases, sealing over unrepaired cracks will actually accelerate pavement deterioration rather than improving it. As temperature changes cause the driveway surface to expand and contract, movement will eventually cause the sealant over cracks to split and peel away. This exposes the original cracks, allowing them spread wider. Freezing water penetrating under the sealant can also cause cracks to propagate faster.
Once sealant begins failing at cracks, it is exposed to fuels, oils and UV damage and will deteriorate rapidly. Attempting to simply reapply more sealant over unfilled cracks starts a cycle of sealing and resealing that becomes increasingly less effective. For longevity, cracks should always be filled properly before sealing.
Can cracks reappear after filling?
It’s common for some cracks to reappear in driveways after an initial filling. Asphalt and concrete continue to shift and settle for several years as part of the curing process. However, filled cracks are much more stable than unfilled ones. They are able to flex and resist widening or spreading. Proper crack filling extends the life of repairs significantly.
To maintain a sound driveway, it is necessary to remain vigilant in identifying new cracks or movement at patched areas. Any new fissures appearing after repairs should be filled again before resealing. Repeating the crack fill and sealant process approximately every 2 to 8 years will maintain the integrity of the pavement.
Will sealant fill small cracks?
Driveway sealant is formulated to penetrate pores on the very surface of pavement. It will likely penetrate hairline cracks less than 1/8 inch that only go partway through the upper layer of asphalt or concrete. This can provide some water resistance in fine spiderweb cracking.
However, sealant lacks the body and adhesion to sink deeper into cracks and bond to the sides. Cracks that go deeper than the top 1/16 to 1/8 inch require a thicker filler like caulk or epoxy for proper repair. While sealant may hide some hairline cracks, it is not considered an adequate crack filling material.
Should all cracks be filled?
As a general rule, all cracks wider than 1/8 inch should be properly filled with a suitable material before sealing a driveway. Very fine hairline cracks may only require sealing. However, paying close attention to thorough crack repairs will always provide longer lasting results.
Even hairline spiderweb cracking patterns that look like a series of very fine interconnected cracks can allow moisture penetration. Water will find the smallest openings leading to subsurface damage. Taking the time to clean and fill all types of cracks before sealing is the best practice.
How soon can you seal after filling cracks?
It’s important to allow adequate curing time for all crack fillers before applying sealant. This varies from 2 hours to 2 days depending on temperature and product used. Hot, dry conditions allow faster curing. Shorter curing times are generally required for liquid fillers compared to caulks.
Review manufacturer instructions to determine recommended curing times. Test cured cracks with slight pressure from a finger to confirm they are no longer tacky before sealing. Insufficient curing could cause sealant not to adhere properly in repaired areas.
Can you seal a driveway with cracks?
Technically sealant can be applied over cracked driveways, but the results will only be temporary. Without filling cracks first, sealant will quickly begin failing as temperature changes enlarge cracks. Constant expansion and contraction of pavement will cause sealant to peel and flake off.
While covering a cracked driveway with sealant provides a short term improvement in appearance, it does not prevent ongoing deterioration. For the most effective, longest lasting sealcoat, every crack wider than 1/8 inch should first be cleaned and filled before applying any sealer.
Conclusion
While sealing fills the microscopic pores in pavement, it does not have the properties needed to repair larger cracks and damaged areas in driveways. Before sealing, all cracks wider than 1/8 inch must be filled with appropriate caulks, epoxies or patch materials based on the crack size and driveway type. Proper filling provides structural repairs that stabilize cracks and prevent water intrusion leading to more damage.
Sealing over unrepaired cracks is only a quick, temporary fix. It masks cracks visually but allows them to worsen over time as sealant prematurely fails. Taking the time to clean and fill all cracks before applying a fresh sealant coating is the only way to extend the life of driveways long-term. Following this critical order of operations will provide lasting protection and beauty.
