Don't Demolish An Uneven Walkway: Slabjack it!
Uneven, cracked concrete driveways and walkways are dangerous and unsightly. Left unchecked - cracked, uneven sidewalks, and concrete slabs can be trip-and-fall hazards and may impede water flow.
As the concrete slab settles, it can sink into the ground, developing uneven spots or even cracking. This poses a risk to you and others, and it can threaten the structural integrity of any structures that are built over it.
Although concrete is durable, it is not indestructible. Over time, a variety of factors can affect the look or function of concrete slabs and lead to cracking, sinking, or failure. If your concrete starts sinking, you have two primary options: leveling and lifting or replacement.
Slabjacking
Slabjacking is a concrete repair method that utilizes restorative technology to lift and level a sunken concrete slab. This repair is accomplished by drilling a hole in the concrete and pumping a substance through the concrete in effort to lift it up and create a level appearance.
Lifting concrete is an affordable, minimally invasive option that lifts the concrete back into the proper position without damaging it, and without the need to remove and replace it. It is fast, effective, and efficient.
Polyurethane Leveling Process
Standardly, a ⅝” hole is drilled through the slab while a delivery port is installed into the same ⅝” hole. The polyurethane injection connects to the port and delivers the lifting material through the port and underneath the concrete slab. As the polyurethane material expands it begins to raise the concrete.
Drill 5/8” size holes in the uneven slab
Insert the foam injection ports
Using the ports, inject the expanding polyurethane foam
As the polyurethane foam expands, be sure that the concrete slab is centered and level with its adjacent slabs
After all slabs are leveled, finish the job by patching and smoothing the drilled holes for a seamless look
This leveling process is done slowly, and methodically. After each incremental application, the contractor measures to be certain that the slab is at the precise height and level with its surrounding slabs, until the process is complete.
Benefits
Fast results: The foam is capable of supporting weight and reaches its full strength in just 15 minutes
Non-invasive: There is no need to destroy and remove the existing concrete, and there is less mess than with conventional lifting methods using slurry
Lightweight: Once installed, polyurethane lifting foam weighs just four to six pounds per cubic foot compared to the 120 pounds per cubic foot that traditional fill material weighs
Waterproof: After installation, there is no risk of wash-out, and the foam will be unaffected by freeze and thaw cycles
Environmental friendliness: Polyurethane foam releases no harmful chemicals and will not react with the soil
Drawback
More expensive than mudjacking
Mudjacking
Mudjacking is much like the polyurethane method, but uses a mud-like mixture instead of polyurethane to lift the concrete slab.
The mud mixture is injected through 1" cut outs in the slab
The force of the mixture beneath the slab applies just enough pressure to slowly push the concrete slab up and back in place to its leveled height
Often a water, sand and concrete mixture is used, or in some cases a crushed limestone mixture
This low pressure method of raising the slab allows the contractor an appropriate amount of time to lift, measure, and lift more, until the slab is at an even height
This mud slurry is injected under the concrete slabs with a transportable pump
Benefit
Mudjacking tends to be less expensive vs. the polyurethane method
Drawbacks
Requires a lot of additional clean up
Requires large holes to be drilled in to the concrete slab
Tends to be a slow process due to the mixing and maneuvering of the pump
Why Does Concrete Sink and Crack?
The ravages of time, temperature changes, erosion, and moisture intrusion can all take a heavy toll on concrete slabs. In most cases, an uneven slab settles as a result of natural soil changes. High water content in the soil expands and contracts with repeated freezes and thaws, and the concrete shifts and settles. Occasionally, poor drainage conditions cause the soil to wash out beneath the slab, creating a void into which the slab eventually settles and sinks.
Other things that can lead to sinking and cracking include:
Drying shrinkage, which occurs when a slab is restrained during the drying process
Chemical reactions due to weathering or exposure to certain chemicals
Poor construction
Tree roots
Air pocket development
Exposure to weather extremes
Spotting problems early and addressing them promptly can help you prevent more serious issues later.
Signs Concrete is Sinking
The slab may be uneven or have a sharp edge jutting out of the ground. Sometimes the signs are a little more subtle but this can still be dangerous, causing trips or falls or even structural damage.
Checking your property periodically for signs of sinking or failing concrete can help you catch problems before they get out of control. Look for:
Uneven concrete walkways and sidewalk slabs
Settling driveways
Sunken or tilted steps
Damp or flooded basements due to settling concrete patios
Poor drainage and water runoff elsewhere
A slab that seems to rock when driven over
A slab that seems hollow or sounds as if a void has developed below it
Cracks between the driveway and the street
Cracks in the foundation
Cracks or weeds growing through the patio
Cracks in your pool deck
Slabjack Vs. Demolish and Pour New
Why Slabjack?
Your property might be a candidate for slabjacking if:
Your concrete is intact and in good condition
The sunken concrete does not extend over a large area
The concrete is less than 15 years old
Strong, intact concrete is a better candidate for this repair processes than older concrete that may have other structural problems.
Demolish and Pour New
However, lifting and leveling, or slabjacking is not always the best option, and in some cases, it might not even be possible. In these cases, removal and replacement might be necessary.
You may need to opt for removal and replacement if:
The concrete is old, significantly worn, cracked, broken, or otherwise badly damaged
The sunken concrete covers an extensive area
The concrete has underlying foundation problems
If there are multiple pieces of concrete, think about replacing the entire walkway since leveling each individual slab may not yield the best results.
Slabjacking can correct minor issues, but attempting to slabjack weak or damaged concrete can result in a destroyed slab. In these cases, it is best to removing the old, damaged slab and starting with fresh concrete.
Cost of Slabjacking
Slabjacking tends to be the more cost-effective solution compared to complete slab demolition and replacement, but the costs can vary significantly based on a number of factors, including:
The size and location of the slab
The type and amount of materials needed
The expertise of the company providing the service
Polyeurythane tends to cost more than mudjacking
Cost: Varies by project, but averages about $1,000.
Cost of Demolishing and Rebuilding the Walkway Slab
Demolishing and rebuilding your slab is a much more extensive and invasive project. Some of the elements that will effect your cost will be:
Demolition
Removal of the demolished materials
Braces
Replacement concrete pour
Restored landscaping
Cost: From $1250 to $3000+ / $5 to $15 per square foot depending on your geographic location