Don't Rip It Up! Pour Fresh Concrete Over Your Asphalt Driveway

Does your asphalt driveway look tired and worn with cracks, potholes and crumbling edges? Instead of undertaking a costly full replacement, you can give your existing asphalt driveway new life by resurfacing it with a decorative concrete overlay. Read on to learn the benefits of pouring concrete over asphalt and how to ensure success.

Revive Your Asphalt Driveway without Full Replacement

Asphalt driveways are notorious for developing problems over time. Exposure to the elements, freeze-thaw cycles, vehicle traffic and ground movement below eventually take a toll. Once the asphalt begins to deteriorate, the problems only accelerate.

Rather than rip up and discard your entire asphalt driveway, consider resurfacing it with a fresh concrete overlay. This creates an attractive new surface while saving the cost and hassle of full removal and replacement.

Benefits of Concrete Over Asphalt

• Much lower cost compared to new asphalt or concrete driveway
• Preserves existing asphalt substrate
• Creates a smooth, durable and decorative concrete surface
• Solves issues like cracks, potholes, raveling without replacement
• Can be customized with textures, colors, designs
• Extends life of driveway overall

Keys to Success with a Concrete Overlay

While pouring concrete over asphalt can deliver an affordable resurfacing, there are some important requirements for it to last:

• Asphalt must be in sound condition without excessive cracking or movement
• Proper preparation of the asphalt surface
• Adequate thickness of the concrete layer
• Allowing concrete to cure fully before vehicle use
• Proper control joints cut into concrete to prevent cracking
• Regular maintenance to maximize longevity

When Can You Pour Concrete Over Asphalt?

The existing asphalt must meet certain conditions to be a suitable base for a concrete overlay. The asphalt needs to be in decent shape without major flaws that could compromise the concrete above.

Asphalt Requirements for Concrete Overlay

The asphalt substrate under the concrete overlay should meet these conditions:

• Intact surface without significant cracks, pitting, raveling or deterioration
• Stable base with no evidence of sinking, heaving or movement
• Graded properly for drainage
• At least 2 inches thick; 3-4 inches preferred

If there are only minor cracks, these can be filled and repaired prior to placing the concrete. But major structural issues with the asphalt indicate it won't provide sound long-term support.

Unsuitable Asphalt Conditions

These asphalt problems mean it is NOT a good candidate for a concrete overlay:

• Severe cracking with alligatoring, large splits or uneven sections
• Potholes, crumbling edges, raveling surface
• Evidence of sinking, heaving or ground movement
• Deterioration from lack of maintenance, weathering, wear
• Less than 2 inches thick

With underlying asphalt in poor shape, any concrete poured over the top will eventually fail. In that case, full removal and replacement of the asphalt is likely the better solution.

Preparing the Asphalt Surface

Proper preparation of the asphalt surface is vital before pouring concrete over it. This ensures a solid bond and prevents water from infiltrating underneath.

Inspect and Repair Asphalt

Carefully inspect the asphalt for any cracks, holes, raveling or other flaws. Use crack filler designed for asphalt to patch any small cracks and holes. Severely deteriorated sections may need removal and repair.

Clean Surface Thoroughly

Power wash the entire asphalt surface to remove any dirt, debris, oil drips or other contaminants. Concrete will not bond effectively to a dirty surface. Avoid any chemical cleaners that could degrade the asphalt.

Create Grid Pattern for Drainage

Use a masonry drill to make holes across the asphalt surface in a grid pattern. This allows water to drain through the concrete and asphalt layers. Spacing holes every few feet prevents water backup.

Anchor Concrete with Rebar

Secure vertical rebar rods into the asphalt using an epoxy or driving through the surface. Horizontal rebar is tied between the vertical rods. This creates a rigid framework to prevent movement between the asphalt and concrete.

Pouring and Finishing the Concrete Overlay

With the proper asphalt base prepared, it's time to mix, pour and finish the decorative concrete overlay.

Minimum Concrete Thickness

The concrete overlay should be at least 4 inches thick over the asphalt. This ensures adequate strength and durability. If vehicle loads will be high, increasing to 6 inches is recommended.

Mix Concrete Properly

Mix the concrete to the correct consistency - too much water will weaken it. A medium slump rating is ideal. Consider additives to increase adhesion and reduce cracking.

Pour and Tool Concrete

Pour the concrete evenly over the surface, then smooth with trowels. For improved traction, add a broom finish. Or create decorative patterns, textures and colors using stamping tools.

Allow Full Curing Time

Concrete reaches full strength over several weeks. Avoid vehicle traffic until it has cured for at least one week to prevent surface damage.

Preventing Bonding Issues

Creating an adequate bond between the concrete overlay and the asphalt is challenging. Take steps to maximize adhesion.

Lack of Mechanical Bond

Unlike concrete on concrete, the asphalt surface is flexible and non-porous. This prevents a strong mechanical bond with the concrete poured over it.

Water Can Damage Bond

Water infiltration between the asphalt and concrete layers will quickly deteriorate the integrity of the bond. Proper drainage and grid holes help prevent this.

Use Admixtures to Improve Bond

Adding latex or acrylic polymers to the concrete mix improves bonding and elasticity to handle movement better.

Rebar Anchors Concrete Firmly

Securing rebar firmly into the asphalt anchors the concrete overlay in place. This prevents shifting or separation of the concrete from the asphalt below.

Avoiding Cracks in the Concrete

Cracks can develop in concrete over asphalt over time. Control joints are essential to prevent cracking and provide longer service life.

Causes of Cracking

Factors that can cause cracks in concrete over asphalt include:

• Concrete shrinkage as it cures
• Ground settlement under the driveway
• Lack of movement joints in concrete
• Vehicle loads and freeze-thaw cycles

Control Joints in Concrete

Cut control joints into the concrete overlay using a concrete saw. This creates planned weak points where the concrete can crack in an orderly pattern.

• Space control joints every 6-12 feet
• Cut joints within 24 hours of pouring concrete
• Joints should be 1/4 the depth of the concrete

Sealing Concrete Control Joints

Seal control joints with caulk or joint sealant to prevent debris and water intrusion that can cause further cracking. Monitor and re-seal as needed.

Long-Term Maintenance

While poured concrete lasts many years, regular maintenance and care is required to achieve maximum longevity of a concrete overlay.

Regular Cleaning

Sweep or blow debris from the concrete routinely. Pressure wash occasionally to prevent staining. Avoid harsh chemical cleaners.

Re-Sealing Every 1-2 Years

Ensure joints stay properly sealed by reapplying caulk/sealant every year or two. This prevents moisture penetration to the asphalt layer underneath.

Prompt Crack Repair

Check for any new cracks or damage annually. Repair quickly to prevent further deterioration. Routing and sealing cracks properly extends the service life.

Limit Freeze-Thaw Cycles

Reduce use of deicing salts that can damage concrete and degrade the asphalt over time. Use sand for added winter traction instead.

Is Concrete Over Asphalt Right for You?

Consider these factors when deciding if resurfacing your asphalt driveway with concrete makes sense:

• Condition of existing asphalt
• Your budget for the project
• How long you plan to stay in the home
• Willingness to perform yearly maintenance

Consulting with a concrete contractor is wise to evaluate your specific scenario. While pouring concrete over asphalt has some risks, the cost savings versus full replacement may make it an ideal solution if done properly.

You can have a beautiful new concrete driveway surface over your existing asphalt base with proper preparation of the asphalt, installation of a thick concrete layer, effective control joints, and care. This spares the cost and work of a full tear-out. Your tired asphalt driveway will be refreshed and renewed without the major hassle of replacement.