Common Questions About Concrete Lifting Foam

Man walking on a broken sidewalk

Common Questions About Concrete Lifting Foam

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Man walking on a broken sidewalk

Common Questions About Concrete Lifting Foam

Click Here
Table of Contents

Concrete lifting foam is often the easiest way to repair an uneven sidewalk or driveway. No need to dig up and replace the uneven slab when concrete lifting foam is faster and less expensive.

In this article, we’re going to talk about why concrete slabs become uneven, what is concrete lifting foam, how lifting foam works, and more.

What Causes Concrete To Sink?

Concrete slabs become uneven for various reasons, including:

  • Unstable soil under the slab – Many times, this is because of poor drainage and erosion under the slab. As the soil moves around, voids form, and the slab sinks into them and becomes uneven.
  • Wear and tear – Over time, traffic on top of the slab will compress it into the soil, and this could cause it to become unlevel.
  • Invasive tree roots – We’ve all seen tree roots pushing up on a slab, causing it to become uneven.

What Is Concrete Lifting Foam?

Concrete lifting foam is a synthetic, waterproof material strong enough to lift and level concrete slabs like sidewalks, driveways, pool decks, patios, garage floors, warehouse floors, highways, etc. After the repair is complete, the concrete slab is strong enough for pedestrians and vehicles.

What Is Concrete Lifting?

Concrete lifting involves using polyurethane concrete lifting foam to fill voids and level an uneven slab. Lifting foam is a newer way of fixing an uneven slab. An older technique called “mudjacking” uses a slurry containing a mixture of cement, sand, and soil. The slurry looks like mud, and that’s why it’s called mudjacking. While mudjacking isn’t as popular as it once was, it’s still being used to lift concrete slabs. We’ll talk about the difference between lifting foam and mudjacking below.

How Does Lifting Foam Work?

Releveling an uneven slab using concrete lifting foam works as follows:

  • Small, dime-sized holes are drilled into the uneven slab.
  • These holes are used to inject the concrete lifting foam under the slab.
  • The lifting foam immediately begins to expand, lifting the uneven slab and compressing loose soil.
  • After the uneven slab has been lifted and leveled, the holes are patched with a compound matching the slab.
  • Fifteen minutes after the repair is complete, the slab is ready for use again.
how does concrete lifting foam work kc waterproofing infographic

Polyurethane Foam Injection vs. Mudjacking

Both polyurethane foam injection and mudjacking are ways to lift and level a sunken concrete slab. In both cases, a material is injected under the concrete through holes drilled in the slab. While mudjacking uses a cement slurry, polyurethane foam injection uses a liquid that turns to foam. This waterproof, synthetic material expands under the slab and then hardens. Unlike the cement slurry in mudjacking, concrete lifting foam won’t break down over time. Therefore, the repair lasts longer.

While polyurethane foam injection is more popular today for leveling uneven concrete slabs, mudjacking is still being used. The holes used to inject the mudjacking slurry under the concrete are a bit larger – up to 2 inches – than those drilled for polyurethane foam injection which are usually around 5/8 inch. Also, repairing an uneven slab using mudjacking isn’t as fast as repairing it with lifting foam. After mudjacking is complete, it can take up to 24 hours before the slab is ready to be used again.

While mudjacking is less expensive than polyurethane foam injection, it doesn’t last as long. This is because the slurry is subject to erosion which can cause the slab to become uneven again. Of course, if there’s a lot of movement in the soil, even concrete lifting foam can move and cause the slab to sink again. However, this isn’t that common.

For more information see, What is Concrete Foam Jacking?

Why Do Some Contractors Say Mudjacking is Better Than Concrete Lifting Foam?

Some contractors out there prefer to lift uneven concrete slabs via the cement slurry used in mudjacking rather than the concrete lifting foam used in polyurethane foam injection. While some just like the fact that mudjacking uses a natural – rather than synthetic – material, others claim that the cement slurry used in mudjacking actually does a better job of lifting and leveling a sunken concrete slab. Here’s how we see things at KC Waterproofing and Foundation Repair:

Claim: Polyurethane foam injection expands too fast and doesn’t fill all the voids under the slab. Therefore, mudjacking, which expands slower once injected under the slab, is the better repair solution.

Truth: We can adjust the concrete lifting foam’s expansion speed by lowering the temperature of the foam. This will cause it to expand more slowly, filling all voids.

Claim: Mudjacking uses a natural material to lift the concrete, while concrete lifting foam is toxic.

Truth: While one element of concrete lifting foam is slightly toxic by itself, combining it with the other element makes the resulting product safe for humans and pets. Combining the two elements happens before the concrete lifting foam comes out of the nozzle. Therefore, the foam injected under the concrete is safe.

Claim: Mudjacking lasts longer than polyurethane foam injection.

Truth: The lifting foam used in polyurethane foam injection is stronger because it’s a synthetic material that won’t break down over time. The cement slurry used in mudjacking is heavier and, therefore, more likely to cause the slab to become unlevel again.

Claim: Mudjacking is less expensive.

Truth: Mudjacking is less expensive in the short term. However, since it doesn’t last as long as lifting foam, the repair will need to be redone more often. That adds up to a more expensive repair in the long run.

Overall, polyurethane foam injection is a faster repair that uses smaller holes. It lasts longer than mudjacking because concrete lifting foam is a synthetic material. Mudjacking uses a heavy cement slurry than could cause the slab to sink again. While mudjacking may be a natural material, that means it’s more susceptible to erosion, and that means another uneven slab.

How Much Does Concrete Lifting Cost?

Lifting and leveling a concrete slab using concrete lifting foam is more expensive than mudjacking. However, it lasts longer. It’s also less expensive than digging up the old slab and pouring fresh concrete.

Of course, the cost of releveling a concrete slab will depend on where you live and the size of the area that needs releveling. Larger areas need more foam, and this increases the cost.

The only way to know how much it will cost to raise your uneven concrete slab is to contact a foundation repair contractor that does concrete leveling and ask for an inspection and repair estimate.

Do you have an uneven sidewalk, driveway, pool deck, patio, or some other type of concrete slab? Contact us today for an inspection and estimate if you’re in our Kansas City, MO, service area.



Don Derry, Jr. is the owner of KC Waterproofing & Foundation Repair. Don became an entrepreneur at the age of 18 and has operated a successful business in Kansas City for nearly 40 years. His vision for the company has always been to help property owners protect their investment and valuables from foundation, structural and water control problems. KC Waterproofing & Foundation Repair continues to lead the way in cutting edge technologies. Structural piering, wall anchoring, foundation underpinning, interior and exterior drainage control, new construction waterproofing and poly injections for slab stabilization are among the top services provided.