Uneven Concrete Slab Repairs Using Polyurethane Foam Injection

Searching for information about concrete slab repairs? If so, don’t hit that back button because you’ve landed on the right page. In this article, we’re going to talk about uneven concrete slab repairs using a repair technique called polyurethane foam injection. We’re also going to go over why concrete slabs become uneven, why concrete slab repairs are usually better than digging up and replacing a slab, and more.

Why Do Concrete Slabs Become Uneven?

Concrete slabs such as sidewalks, driveways, and patios, usually become uneven for one of the following reasonsConcrete slabs such as sidewalks, driveways, and patios, usually become uneven for one of the following reasons:

  • Expansive soil – Expansive soil is clay-rich and for this reason expands as it soaks up moisture, and then shrinks as it loses moisture and dries out. This swelling/shrinking – which can be caused by drought/non-drought periods – causes movement in the soil under the slab, and will often cause a slab to become uneven over time.
  • Erosion under the slab – Some types of soil are prone to erosion and if there’s poor drainage under the slab, this could cause voids to form and an uneven slab eventually.
  • Soil not tamped down – Soil always needs to be properly compacted before anything gets placed or built on top of it, including concrete slabs. If this isn’t done, the slab could settle into the soil and end up uneven.
  • Tree roots – We’ve all seen examples of tree roots pushing up on a slab and causing it to become unlevel.
  • Dead leaves decaying leave voids – Leaves and other organic matter should be removed from the soil before a concrete slab is poured. If this isn’t done, voids could form under the slab. If the slab sinks into the voids, it will become uneven.

Uneven Concrete Slab Repairs Using Polyurethane Foam Injection

Fortunately, an uneven concrete slab can be repaired (i.e, leveled) in just a few hours using polyurethane foam injection, a waterproof material that’s injected under the slab in order to level it. Polyurethane foam injection can lift and level sidewalks, driveways, patios, pool decks, and more.

The general polyurethane foam injection procedure to perform concrete slab repairs is as follows:

  • Dime-sized holes are drilled into the affected slab.
  • A nozzle is inserted through the holes and the polyurethane foam is injected under the slab.
  • The foam immediately begins to expand, fills any voids, and raises the slab.
  • The holes are patched using a compound that matches the color of the concrete.
  • Fifteen minutes after the repair is complete, the slab is ready for use.

Is Polyurethane Foam Better Than Mudjacking?

Yes, we believe polyurethane foam injection is better than mudjacking. Mudjacking is an older method for leveling an uneven concrete slab. Today, most concrete leveling jobs are done using polyurethane foam injection for the following reasons:

most concrete leveling jobs are done using polyurethane foam injection

  • The mudjacking slurry used to raise the slab is heavy because it contains cement, sand, soil, etc. Because of this it has the potential to make the problem even worse because the slab might have become uneven because weak soil was unable to support it. If so, adding more weight to the soil in the form of a cement slurry isn’t going to help.
  • The mudjacking slurry is prone to erosion if there’s poor drainage under the slab.
  • The holes used to inject the mudjacking slurry under the slab are at least 2 inches wide. Compare this with the dime-sized holes used with polyurethane foam injection.
  • Mudjacking is a messy process and then it takes 2-3 to dry and harden. This means downtime.

Yes, mudjacking is still being done today. However, we view it as a temporary fix, at best.

Are Concrete Slab Repairs Better Than Replacing The Slab?

Workmen leveling fresh Concrete with concrete leveling tool, newly poured concrete sidewalk on a building site. An wooden bull float is being used to smooth a new sidewalk.

Unless the concrete slab is severely damaged, yes, lifting the slab via polyurethane foam injection is better than digging up and replacing the slab. Concrete leveling using polyurethane foam is a quick procedure taking usually no more than a few hours and then the slab is ready for use. Pouring a new slab and then waiting for it to dry and harden takes time. Replacing a slab is also more expensive. Therefore, it’s a repair for those times when the slab is so severely damaged that leveling using polyurethane foam isn’t an option.

How Much Do Uneven Concrete Slab Repairs Cost?

The cost to fix an uneven concrete slab using polyurethane foam injection depends on where you live and the size of the affected area (this determines how much lifting foam is needed).

How To Help Prevent Concrete Slabs From Becoming Uneven

You can help prevent a concrete slab – such as a sidewalk or driveway – from becoming uneven – by doing the following:

  • Make sure the soil is adequately tamped down before the slab gets poured on top of it.
  • Ensure that any organic material such as leaves, is removed from the soil before the slab gets poured.
  • Make sure there’s good drainage under and around the slab.
  • Keep trees with invasive root systems away from the slab.

If you have an uneven concrete slab that needs to be lifted and leveled – and you’re in our Southern California and Arizona service area – contact us today and schedule an evaluation.


Brian Dalinghaus

Brian is one of the Co-Founders of Dalinghaus Construction. He has been in the foundation repair industry since 2005. During his career, he has been associated with helping over 4,000 homes and structures throughout California and Arizona.

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